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  </style><style type="text/css" style="display: none !important;">#A9AdsMiddleBoxTop, #A9AdsOutOfStockWidgetTop, #A9AdsServicesWidgetTop, #AdContainerTop, #AdHeader, #AdMiddle, #AdRectangle, #AdShowcase_F1, #AdSky23, #AdSkyscraper, #AdSponsor_SF, #AdText, #Ad_Block, #Ad_Center1, #Ad_Top, #Adbanner, #Adrectangle, #AdsContent, #AdsWrap, #AdvertMPU23b, #AdvertiseFrame, #Advertorial, #BigBoxAd, #CompanyDetailsNarrowGoogleAdsPresentationControl, #CompanyDetailsWideGoogleAdsPresentationControl, #ContentAd, #ContentAd1, #ContentAd2, #ContentAdPlaceHolder1, #ContentAdPlaceHolder2, #FooterAd, #FooterAdContainer, #HEADERAD, #HeaderAdsBlock, #HeroAd, #HouseAd, #LeftAdF1, #LeftAdF2, #PageLeaderAd, #RightSponsoredAd, #SectionAd300-250, #SidebarAdContainer, #SkyAd, #SponsoredAd, #TOP_ADROW, #TopAdPos, #VM-MPU-adspace, #VM-header-adwrap, #XEadLeaderboard, #XEadSkyscraper, #ad-160x600, #ad-250x300, #ad-300x250, #ad-300x250Div, #ad-728, #ad-banner, #ad-bottom, #ad-container, #ad-footer, #ad-footprint-160x600, #ad-front-footer, #ad-front-sponsoredlinks, #ad-halfpage, #ad-label, #ad-leaderboard, #ad-leaderboard-bottom, #ad-leaderboard-top, #ad-left, #ad-lrec, #ad-medium-rectangle, #ad-middlethree, #ad-middletwo, #ad-mpu, #ad-placard, #ad-rectangle, #ad-righttop, #ad-skyscraper, #ad-space, #ad-splash, #ad-target, #ad-target-Leaderbord, #ad-top, #ad-tower, #ad-typ1, #ad-wrap, #ad-wrap-right, #ad-wrapper1, #ad-yahoo-simple, #ad1, #ad125x125, #ad160x600, #ad160x600right, #ad1Sp, #ad2, #ad2Sp, #ad3, #ad300, #ad300-250, #ad300_x_250, #ad300x150, #ad300x250, #ad300x250Module, #ad300x60, #ad336, #ad375x85, #ad526x250, #ad600, #ad728x90, #adB, #adBanner, #adBanner120x600, #adBannerTable, #adBar, #adContainer, #adFps, #adFtofrs, #adGroup1, #adHeader, #adL, #adLB, #adMiddle0Frontpage, #adMiniPremiere, #adPlaceHolderRight, #adSenseModule, #adServer_marginal, #adSky, #adSlider, #adSpace300_ifrMain, #adSpace_footer, #adSpace_top, #adSpecial, #adSpot-Leader, #adSpot-banner, 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{ visibility:hidden !important;    display:none !important; }</style><body onload="init()"><div class="head" id="head">
   <p><a href="http://www.w3.org/"><img alt="W3C" height="48" src="./HTML5_files/w3c_home" width="72"></a></p>

   <h1>HTML5</h1>
   <h2 class="no-num no-toc" id="a-vocabulary-and-associated-apis-for-html-and-xhtml">A vocabulary and associated APIs for HTML and XHTML</h2>
   <h2 class="no-num no-toc" id="w3c-working-draft-16-november-2010">W3C Working Draft 16 November 2010</h2>
   <dl><dt>This Version:</dt>
    <dd><a href="http://www.w3.org/TR/2010/WD-html5-20101116/">http://www.w3.org/TR/2010/WD-html5-20101116/</a></dd>
    <dt>Latest Published Version:</dt>
    <dd><a href="http://www.w3.org/TR/html5/">http://www.w3.org/TR/html5/</a></dd>
    <dt>Latest Editor's Draft:</dt>
    <dd><a class="latest-link" href="./HTML5_files/HTML5.htm">http://dev.w3.org/html5/spec/Overview.html</a></dd>
<!-- ZZZ: add the new version after it has shipped -->
    <dt>Previous Versions:</dt>
    <dd><a href="http://www.w3.org/TR/2010/WD-html5-20100624/">http://www.w3.org/TR/2010/WD-html5-20100624/</a></dd>
    <dd><a href="http://www.w3.org/TR/2010/WD-html5-20100304/">http://www.w3.org/TR/2010/WD-html5-20100304/</a></dd>
    <dd><a href="http://www.w3.org/TR/2009/WD-html5-20090825/">http://www.w3.org/TR/2009/WD-html5-20090825/</a></dd>
    <dd><a href="http://www.w3.org/TR/2009/WD-html5-20090423/">http://www.w3.org/TR/2009/WD-html5-20090423/</a></dd>
    <dd><a href="http://www.w3.org/TR/2009/WD-html5-20090212/">http://www.w3.org/TR/2009/WD-html5-20090212/</a></dd>
    <dd><a href="http://www.w3.org/TR/2008/WD-html5-20080610/">http://www.w3.org/TR/2008/WD-html5-20080610/</a></dd>
    <dd><a href="http://www.w3.org/TR/2008/WD-html5-20080122/">http://www.w3.org/TR/2008/WD-html5-20080122/</a></dd>
<!-- :ZZZ -->
    <dt>Editors:</dt>
    <dd><a href="mailto:ian@hixie.ch">Ian Hickson</a>, Google, Inc.</dd>
   </dl><p>This specification is available in the following formats: 
    <a href="./HTML5_files/HTML5.htm">single page HTML</a>,
    <a href="http://dev.w3.org/html5/spec/spec.html">multipage HTML</a>,
    <a href="http://dev.w3.org/html5/spec/author/">web developer edition</a>.
    This is revision $Revision: 1.4550 $.
   </p> 
     <p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
   © 2010 <a href="http://www.w3.org/"><abbr title="World Wide
   Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts
   Institute of Technology">MIT</abbr></a>, <a href="http://www.ercim.org/"><abbr title="European Research
   Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C
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   use</a> rules apply.</p>


   <!-- UNDER NO CIRCUMSTANCES IS THE FOLLOWING PARAGRAPH TO BE REMOVED OR EDITED WITHOUT TALKING TO IAN FIRST -->
   <p class="alt">The bulk of the text of this specification is also
   available in the WHATWG <a href="http://www.whatwg.org/specs/web-apps/current-work/complete.html">Web Applications 1.0</a> specification, under a license that permits
   reuse of the specification text.</p>
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  </div><hr class="top"><h2 class="no-num no-toc" id="abstract">Abstract</h2><p>This specification defines the 5th major revision of the core
  language of the World Wide Web: the Hypertext Markup Language
  (HTML). In this version, new features are introduced to help Web
  application authors, new elements are introduced based on research
  into prevailing authoring practices, and special attention has been
  given to defining clear conformance criteria for user agents in an
  effort to improve interoperability.</p><h2 class="no-num no-toc" id="status-of-this-document">Status of This document</h2><!-- intro boilerplate (required) --><p><em>This section describes the status of this document at the
  time of its publication. Other documents may supersede this
  document. A list of current W3C publications and the most recently
  formally published revision of this technical report can be found in
  the <a href="http://www.w3.org/TR/">W3C technical reports index</a>
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  that is tracked by the W3C, please submit them via using <a href="http://www.w3.org/Bugs/Public/enter_bug.cgi?product=HTML%20WG">our
  public bug database</a>. If you do not have an account then you can
  enter feedback using this form:</p><form action="http://www.whatwg.org/specs/web-apps/current-work/file-spam.cgi" method="post">
   <fieldset><legend>Feedback Comments</legend>
    <input name="id" type="hidden" value="top"><input name="component" type="hidden" value="HTML Canvas 2D Context (editor: Ian Hickson)"><input name="response" type="hidden" value="html"><p><label for="feedbackBox">Please enter your feedback, carefully
    indicating the title of the section for which you are submitting
    feedback, quoting the text that's wrong today if appropriate. If
    you're suggesting a new feature, it's really important to say
    <em>what</em> the problem you're trying to solve is. That's more
    important than the solution, in fact.</label></p>
    <p><textarea cols="79" id="feedbackBox" name="text" rows="10"></textarea></p>
    <p class="note">Please don't use section numbers as these tend to
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  </dl><!-- UNDER NO CIRCUMSTANCES IS THE PRECEDING LIST TO BE REMOVED OR EDITED WITHOUT TALKING TO IAN FIRST --><!-- status of document, group responsible (required) --><p>The W3C <a href="http://www.w3.org/html/wg/">HTML Working
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  specification's progress along the W3C Recommendation
  track.
  This specification is the 16 November 2010 WD.
  </p><!-- UNDER NO CIRCUMSTANCES IS THE PRECEDING PARAGRAPH TO BE REMOVED OR EDITED WITHOUT TALKING TO IAN FIRST --><!-- relationship to other work (required) --><p>Work on this specification is also done at the <a href="http://www.whatwg.org/">WHATWG</a>. The W3C HTML working group
  actively pursues convergence with the WHATWG, as required by the <a href="http://www.w3.org/2007/03/HTML-WG-charter">W3C HTML working
  group charter</a>.</p><!-- UNDER NO CIRCUMSTANCES IS THE FOLLOWING PARAGRAPH TO BE REMOVED OR EDITED WITHOUT TALKING TO IAN FIRST --><!-- required patent boilerplate --><p>This document was produced by a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5
  February 2004 W3C Patent Policy</a>. W3C maintains a <a href="http://www.w3.org/2004/01/pp-impl/40318/status" rel="disclosure">public list of
  any patent disclosures</a> made in connection with the deliverables
  of the group; that page also includes instructions for disclosing a
  patent. An individual who has actual knowledge of a patent which the
  individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
  Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
  6 of the W3C Patent Policy</a>.</p><h2 class="no-num no-toc" id="contents">Table of Contents</h2>
<!--begin-toc-->
<ol class="toc">
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction"><span class="secno">1 </span>Introduction</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#background"><span class="secno">1.1 </span>Background</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#audience"><span class="secno">1.2 </span>Audience</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#scope"><span class="secno">1.3 </span>Scope</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#history-1"><span class="secno">1.4 </span>History</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#design-notes"><span class="secno">1.5 </span>Design notes</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#serializability-of-script-execution"><span class="secno">1.5.1 </span>Serializability of script execution</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#compliance-with-other-specifications"><span class="secno">1.5.2 </span>Compliance with other specifications</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#html-vs-xhtml"><span class="secno">1.6 </span>HTML vs XHTML</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#structure-of-this-specification"><span class="secno">1.7 </span>Structure of this specification</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#how-to-read-this-specification"><span class="secno">1.7.1 </span>How to read this specification</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#typographic-conventions"><span class="secno">1.7.2 </span>Typographic conventions</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#a-quick-introduction-to-html"><span class="secno">1.8 </span>A quick introduction to HTML</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#conformance-requirements-for-authors"><span class="secno">1.9 </span>Conformance requirements for authors</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#presentational-markup"><span class="secno">1.9.1 </span>Presentational markup</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#syntax-errors"><span class="secno">1.9.2 </span>Syntax errors</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#restrictions-on-content-models-and-on-attribute-values"><span class="secno">1.9.3 </span>Restrictions on content models and on attribute values</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#recommended-reading"><span class="secno">1.10 </span>Recommended reading</a></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#infrastructure"><span class="secno">2 </span>Common infrastructure</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#terminology"><span class="secno">2.1 </span>Terminology</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#resources"><span class="secno">2.1.1 </span>Resources</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#xml"><span class="secno">2.1.2 </span>XML</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#dom-trees"><span class="secno">2.1.3 </span>DOM trees</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#scripting-0"><span class="secno">2.1.4 </span>Scripting</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#plugins"><span class="secno">2.1.5 </span>Plugins</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#character-encodings"><span class="secno">2.1.6 </span>Character encodings</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#conformance-requirements"><span class="secno">2.2 </span>Conformance requirements</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#dependencies"><span class="secno">2.2.1 </span>Dependencies</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#extensibility"><span class="secno">2.2.2 </span>Extensibility</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#case-sensitivity-and-string-comparison"><span class="secno">2.3 </span>Case-sensitivity and string comparison</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#utf-8"><span class="secno">2.4 </span>UTF-8</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#common-microsyntaxes"><span class="secno">2.5 </span>Common microsyntaxes</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#common-parser-idioms"><span class="secno">2.5.1 </span>Common parser idioms</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#boolean-attributes"><span class="secno">2.5.2 </span>Boolean attributes</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#keywords-and-enumerated-attributes"><span class="secno">2.5.3 </span>Keywords and enumerated attributes</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#numbers"><span class="secno">2.5.4 </span>Numbers</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#non-negative-integers"><span class="secno">2.5.4.1 </span>Non-negative integers</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#signed-integers"><span class="secno">2.5.4.2 </span>Signed integers</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#real-numbers"><span class="secno">2.5.4.3 </span>Real numbers</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#percentages-and-dimensions"><span class="secno">2.5.4.4 </span>Percentages and lengths</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#lists-of-integers"><span class="secno">2.5.4.5 </span>Lists of integers</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#lists-of-dimensions"><span class="secno">2.5.4.6 </span>Lists of dimensions</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#dates-and-times"><span class="secno">2.5.5 </span>Dates and times</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#months"><span class="secno">2.5.5.1 </span>Months</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#dates"><span class="secno">2.5.5.2 </span>Dates</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#times"><span class="secno">2.5.5.3 </span>Times</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#local-dates-and-times"><span class="secno">2.5.5.4 </span>Local dates and times</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#global-dates-and-times"><span class="secno">2.5.5.5 </span>Global dates and times</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#weeks"><span class="secno">2.5.5.6 </span>Weeks</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#vaguer-moments-in-time"><span class="secno">2.5.5.7 </span>Vaguer moments in time</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#colors"><span class="secno">2.5.6 </span>Colors</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#space-separated-tokens"><span class="secno">2.5.7 </span>Space-separated tokens</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#comma-separated-tokens"><span class="secno">2.5.8 </span>Comma-separated tokens</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#syntax-references"><span class="secno">2.5.9 </span>References</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#mq"><span class="secno">2.5.10 </span>Media queries</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#urls"><span class="secno">2.6 </span>URLs</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#terminology-0"><span class="secno">2.6.1 </span>Terminology</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#dynamic-changes-to-base-urls"><span class="secno">2.6.2 </span>Dynamic changes to base URLs</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#interfaces-for-url-manipulation"><span class="secno">2.6.3 </span>Interfaces for URL manipulation</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#fetching-resources"><span class="secno">2.7 </span>Fetching resources</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#concept-http-equivalent"><span class="secno">2.7.1 </span>Protocol concepts</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#encrypted-http-and-related-security-concerns"><span class="secno">2.7.2 </span>Encrypted HTTP and related security concerns</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#content-type-sniffing"><span class="secno">2.7.3 </span>Determining the type of a resource</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#common-dom-interfaces"><span class="secno">2.8 </span>Common DOM interfaces</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#reflecting-content-attributes-in-idl-attributes"><span class="secno">2.8.1 </span>Reflecting content attributes in IDL attributes</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#collections-0"><span class="secno">2.8.2 </span>Collections</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#htmlcollection-0"><span class="secno">2.8.2.1 </span>HTMLCollection</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#htmlallcollection-0"><span class="secno">2.8.2.2 </span>HTMLAllCollection</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#htmlformcontrolscollection-0"><span class="secno">2.8.2.3 </span>HTMLFormControlsCollection</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#htmloptionscollection-0"><span class="secno">2.8.2.4 </span>HTMLOptionsCollection</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#domtokenlist-0"><span class="secno">2.8.3 </span>DOMTokenList</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#domsettabletokenlist-0"><span class="secno">2.8.4 </span>DOMSettableTokenList</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#safe-passing-of-structured-data"><span class="secno">2.8.5 </span>Safe passing of structured data</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#domstringmap-0"><span class="secno">2.8.6 </span>DOMStringMap</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#dom-feature-strings"><span class="secno">2.8.7 </span>DOM feature strings</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#exceptions"><span class="secno">2.8.8 </span>Exceptions</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#garbage-collection"><span class="secno">2.8.9 </span>Garbage collection</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#namespaces"><span class="secno">2.9 </span>Namespaces</a></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#dom"><span class="secno">3 </span>Semantics, structure, and APIs of HTML documents</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#documents"><span class="secno">3.1 </span>Documents</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#documents-in-the-dom"><span class="secno">3.1.1 </span>Documents in the DOM</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#security-document"><span class="secno">3.1.2 </span>Security</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#resource-metadata-management"><span class="secno">3.1.3 </span>Resource metadata management</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#dom-tree-accessors"><span class="secno">3.1.4 </span>DOM tree accessors</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#creating-documents"><span class="secno">3.1.5 </span>Creating documents</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#loading-xml-documents"><span class="secno">3.1.6 </span>Loading XML documents</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#elements"><span class="secno">3.2 </span>Elements</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#semantics-0"><span class="secno">3.2.1 </span>Semantics</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#elements-in-the-dom"><span class="secno">3.2.2 </span>Elements in the DOM</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#global-attributes"><span class="secno">3.2.3 </span>Global attributes</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-id-attribute"><span class="secno">3.2.3.1 </span>The <code>id</code> attribute</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-title-attribute"><span class="secno">3.2.3.2 </span>The <code>title</code> attribute</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-lang-and-xml:lang-attributes"><span class="secno">3.2.3.3 </span>The <code title="attr-lang">lang</code> and <code title="attr-xml-lang">xml:lang</code> attributes</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-xml:base-attribute-xml-only"><span class="secno">3.2.3.4 </span>The <code>xml:base</code>
  attribute (XML only)</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-dir-attribute"><span class="secno">3.2.3.5 </span>The <code>dir</code> attribute</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#classes"><span class="secno">3.2.3.6 </span>The <code>class</code> attribute</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-style-attribute"><span class="secno">3.2.3.7 </span>The <code>style</code> attribute</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#embedding-custom-non-visible-data-with-the-data-attributes"><span class="secno">3.2.3.8 </span>Embedding custom non-visible data with the <code title="attr-data-*">data-*</code> attributes</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#element-definitions"><span class="secno">3.2.4 </span>Element definitions</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#attributes"><span class="secno">3.2.4.1 </span>Attributes</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#content-models"><span class="secno">3.2.5 </span>Content models</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#kinds-of-content"><span class="secno">3.2.5.1 </span>Kinds of content</a>
        <ol>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#metadata-content-0"><span class="secno">3.2.5.1.1 </span>Metadata content</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#flow-content-0"><span class="secno">3.2.5.1.2 </span>Flow content</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#sectioning-content-0"><span class="secno">3.2.5.1.3 </span>Sectioning content</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#heading-content-0"><span class="secno">3.2.5.1.4 </span>Heading content</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#phrasing-content-0"><span class="secno">3.2.5.1.5 </span>Phrasing content</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#embedded-content-0"><span class="secno">3.2.5.1.6 </span>Embedded content</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#interactive-content-0"><span class="secno">3.2.5.1.7 </span>Interactive content</a></li></ol></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#transparent-content-models"><span class="secno">3.2.5.2 </span>Transparent content models</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#paragraphs"><span class="secno">3.2.5.3 </span>Paragraphs</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#annotations-for-assistive-technology-products-aria"><span class="secno">3.2.6 </span>Annotations for assistive technology products (ARIA)</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#apis-in-html-documents"><span class="secno">3.3 </span>APIs in HTML documents</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#interactions-with-xpath-and-xslt"><span class="secno">3.4 </span>Interactions with XPath and XSLT</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#dynamic-markup-insertion"><span class="secno">3.5 </span>Dynamic markup insertion</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#opening-the-input-stream"><span class="secno">3.5.1 </span>Opening the input stream</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#closing-the-input-stream"><span class="secno">3.5.2 </span>Closing the input stream</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#document.write"><span class="secno">3.5.3 </span><code title="dom-document-write">document.write()</code></a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#document.writeln"><span class="secno">3.5.4 </span><code title="dom-document-writeln">document.writeln()</code></a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#innerhtml"><span class="secno">3.5.5 </span><code title="dom-innerHTML">innerHTML</code></a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#outerhtml"><span class="secno">3.5.6 </span><code title="dom-outerHTML">outerHTML</code></a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#insertadjacenthtml"><span class="secno">3.5.7 </span><code title="dom-insertAdjacentHTML">insertAdjacentHTML()</code></a></li></ol></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#semantics"><span class="secno">4 </span>The elements of HTML</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-root-element"><span class="secno">4.1 </span>The root element</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-html-element-0"><span class="secno">4.1.1 </span>The <code>html</code> element</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#document-metadata"><span class="secno">4.2 </span>Document metadata</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-head-element-0"><span class="secno">4.2.1 </span>The <code>head</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-title-element-0"><span class="secno">4.2.2 </span>The <code>title</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-base-element"><span class="secno">4.2.3 </span>The <code>base</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-link-element"><span class="secno">4.2.4 </span>The <code>link</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#meta"><span class="secno">4.2.5 </span>The <code>meta</code> element</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#standard-metadata-names"><span class="secno">4.2.5.1 </span>Standard metadata names</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#other-metadata-names"><span class="secno">4.2.5.2 </span>Other metadata names</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#pragma-directives"><span class="secno">4.2.5.3 </span>Pragma directives</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#other-pragma-directives"><span class="secno">4.2.5.4 </span>Other pragma directives</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#charset"><span class="secno">4.2.5.5 </span>Specifying the document's character encoding</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-style-element"><span class="secno">4.2.6 </span>The <code>style</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#styling"><span class="secno">4.2.7 </span>Styling</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#scripting-1"><span class="secno">4.3 </span>Scripting</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#script"><span class="secno">4.3.1 </span>The <code>script</code> element</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#scriptingLanguages"><span class="secno">4.3.1.1 </span>Scripting languages</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#restrictions-for-contents-of-script-elements"><span class="secno">4.3.1.2 </span>Restrictions for contents of <code>script</code> elements</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#inline-documentation-for-external-scripts"><span class="secno">4.3.1.3 </span>Inline documentation for external scripts</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-noscript-element"><span class="secno">4.3.2 </span>The <code>noscript</code> element</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#sections"><span class="secno">4.4 </span>Sections</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-body-element-0"><span class="secno">4.4.1 </span>The <code>body</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-section-element"><span class="secno">4.4.2 </span>The <code>section</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-nav-element"><span class="secno">4.4.3 </span>The <code>nav</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-article-element"><span class="secno">4.4.4 </span>The <code>article</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-aside-element"><span class="secno">4.4.5 </span>The <code>aside</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-h1-h2-h3-h4-h5-and-h6-elements"><span class="secno">4.4.6 </span>The <code>h1</code>, <code>h2</code>,
  <code>h3</code>, <code>h4</code>,
  <code>h5</code>, and <code>h6</code>
  elements</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-hgroup-element"><span class="secno">4.4.7 </span>The <code>hgroup</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-header-element"><span class="secno">4.4.8 </span>The <code>header</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-footer-element"><span class="secno">4.4.9 </span>The <code>footer</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-address-element"><span class="secno">4.4.10 </span>The <code>address</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#headings-and-sections"><span class="secno">4.4.11 </span>Headings and sections</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#outlines"><span class="secno">4.4.11.1 </span>Creating an outline</a></li></ol></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#grouping-content"><span class="secno">4.5 </span>Grouping content</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-p-element"><span class="secno">4.5.1 </span>The <code>p</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-hr-element"><span class="secno">4.5.2 </span>The <code>hr</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-pre-element"><span class="secno">4.5.3 </span>The <code>pre</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-blockquote-element"><span class="secno">4.5.4 </span>The <code>blockquote</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-ol-element"><span class="secno">4.5.5 </span>The <code>ol</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-ul-element"><span class="secno">4.5.6 </span>The <code>ul</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-li-element"><span class="secno">4.5.7 </span>The <code>li</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-dl-element"><span class="secno">4.5.8 </span>The <code>dl</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-dt-element"><span class="secno">4.5.9 </span>The <code>dt</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-dd-element"><span class="secno">4.5.10 </span>The <code>dd</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-figure-element"><span class="secno">4.5.11 </span>The <code>figure</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-figcaption-element"><span class="secno">4.5.12 </span>The <code>figcaption</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-div-element"><span class="secno">4.5.13 </span>The <code>div</code> element</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#text-level-semantics"><span class="secno">4.6 </span>Text-level semantics</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-a-element"><span class="secno">4.6.1 </span>The <code>a</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-em-element"><span class="secno">4.6.2 </span>The <code>em</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-strong-element"><span class="secno">4.6.3 </span>The <code>strong</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-small-element"><span class="secno">4.6.4 </span>The <code>small</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-s-element"><span class="secno">4.6.5 </span>The <code>s</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-cite-element"><span class="secno">4.6.6 </span>The <code>cite</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-q-element"><span class="secno">4.6.7 </span>The <code>q</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-dfn-element"><span class="secno">4.6.8 </span>The <code>dfn</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-abbr-element"><span class="secno">4.6.9 </span>The <code>abbr</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-time-element"><span class="secno">4.6.10 </span>The <code>time</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-code-element"><span class="secno">4.6.11 </span>The <code>code</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-var-element"><span class="secno">4.6.12 </span>The <code>var</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-samp-element"><span class="secno">4.6.13 </span>The <code>samp</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-kbd-element"><span class="secno">4.6.14 </span>The <code>kbd</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-sub-and-sup-elements"><span class="secno">4.6.15 </span>The <code>sub</code> and <code>sup</code> elements</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-i-element"><span class="secno">4.6.16 </span>The <code>i</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-b-element"><span class="secno">4.6.17 </span>The <code>b</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-mark-element"><span class="secno">4.6.18 </span>The <code>mark</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-ruby-element"><span class="secno">4.6.19 </span>The <code>ruby</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-rt-element"><span class="secno">4.6.20 </span>The <code>rt</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-rp-element"><span class="secno">4.6.21 </span>The <code>rp</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-bdi-element"><span class="secno">4.6.22 </span>The <code>bdi</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-bdo-element"><span class="secno">4.6.23 </span>The <code>bdo</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-span-element"><span class="secno">4.6.24 </span>The <code>span</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-br-element"><span class="secno">4.6.25 </span>The <code>br</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-wbr-element"><span class="secno">4.6.26 </span>The <code>wbr</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#usage-summary"><span class="secno">4.6.27 </span>Usage summary</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#edits"><span class="secno">4.7 </span>Edits</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-ins-element"><span class="secno">4.7.1 </span>The <code>ins</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-del-element"><span class="secno">4.7.2 </span>The <code>del</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#attributes-common-to-ins-and-del-elements"><span class="secno">4.7.3 </span>Attributes common to <code>ins</code> and <code>del</code> elements</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#edits-and-paragraphs"><span class="secno">4.7.4 </span>Edits and paragraphs</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#edits-and-lists"><span class="secno">4.7.5 </span>Edits and lists</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#embedded-content-1"><span class="secno">4.8 </span>Embedded content</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-img-element"><span class="secno">4.8.1 </span>The <code>img</code> element</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#alt"><span class="secno">4.8.1.1 </span>Requirements for providing text to act as an alternative for images</a>
        <ol>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#general-guidelines"><span class="secno">4.8.1.1.1 </span>General guidelines</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#a-link-or-button-containing-nothing-but-the-image"><span class="secno">4.8.1.1.2 </span>A link or button containing nothing but the image</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#a-phrase-or-paragraph-with-an-alternative-graphical-representation:-charts-diagrams-graphs-maps-illustrations"><span class="secno">4.8.1.1.3 </span>A phrase or paragraph with an alternative graphical representation: charts, diagrams, graphs, maps, illustrations</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#a-short-phrase-or-label-with-an-alternative-graphical-representation:-icons-logos"><span class="secno">4.8.1.1.4 </span>A short phrase or label with an alternative graphical representation: icons, logos</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#text-that-has-been-rendered-to-a-graphic-for-typographical-effect"><span class="secno">4.8.1.1.5 </span>Text that has been rendered to a graphic for typographical effect</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#a-graphical-representation-of-some-of-the-surrounding-text"><span class="secno">4.8.1.1.6 </span>A graphical representation of some of the surrounding text</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#a-purely-decorative-image-that-doesn-t-add-any-information"><span class="secno">4.8.1.1.7 </span>A purely decorative image that doesn't add any information</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#a-group-of-images-that-form-a-single-larger-picture-with-no-links"><span class="secno">4.8.1.1.8 </span>A group of images that form a single larger picture with no links</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#a-group-of-images-that-form-a-single-larger-picture-with-links"><span class="secno">4.8.1.1.9 </span>A group of images that form a single larger picture with links</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#a-key-part-of-the-content"><span class="secno">4.8.1.1.10 </span>A key part of the content</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#an-image-not-intended-for-the-user"><span class="secno">4.8.1.1.11 </span>An image not intended for the user</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#an-image-in-an-e-mail-or-private-document-intended-for-a-specific-person-who-is-known-to-be-able-to-view-images"><span class="secno">4.8.1.1.12 </span>An image in an e-mail or private document intended for a specific person who is known to be able to view images</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#guidance-for-markup-generators"><span class="secno">4.8.1.1.13 </span>Guidance for markup generators</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#guidance-for-conformance-checkers"><span class="secno">4.8.1.1.14 </span>Guidance for conformance checkers</a></li></ol></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-iframe-element"><span class="secno">4.8.2 </span>The <code>iframe</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-embed-element"><span class="secno">4.8.3 </span>The <code>embed</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-object-element"><span class="secno">4.8.4 </span>The <code>object</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-param-element"><span class="secno">4.8.5 </span>The <code>param</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#video"><span class="secno">4.8.6 </span>The <code>video</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#audio"><span class="secno">4.8.7 </span>The <code>audio</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-source-element"><span class="secno">4.8.8 </span>The <code>source</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-track-element"><span class="secno">4.8.9 </span>The <code>track</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#media-elements"><span class="secno">4.8.10 </span>Media elements</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#error-codes"><span class="secno">4.8.10.1 </span>Error codes</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#location-of-the-media-resource"><span class="secno">4.8.10.2 </span>Location of the media resource</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#mime-types"><span class="secno">4.8.10.3 </span>MIME types</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#network-states"><span class="secno">4.8.10.4 </span>Network states</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#loading-the-media-resource"><span class="secno">4.8.10.5 </span>Loading the media resource</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#offsets-into-the-media-resource"><span class="secno">4.8.10.6 </span>Offsets into the media resource</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-ready-states"><span class="secno">4.8.10.7 </span>The ready states</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#playing-the-media-resource"><span class="secno">4.8.10.8 </span>Playing the media resource</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#seeking"><span class="secno">4.8.10.9 </span>Seeking</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#timed-tracks"><span class="secno">4.8.10.10 </span>Timed tracks</a>
        <ol>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#timed-track-model"><span class="secno">4.8.10.10.1 </span>Timed track model</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#sourcing-in-band-timed-tracks"><span class="secno">4.8.10.10.2 </span>Sourcing in-band timed tracks</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#sourcing-out-of-band-timed-tracks"><span class="secno">4.8.10.10.3 </span>Sourcing out-of-band timed tracks</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#guidelines-for-exposing-cues-in-various-formats-as-timed-track-cues"><span class="secno">4.8.10.10.4 </span>Guidelines for exposing cues in various formats as
  timed track cues</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#timed-track-api"><span class="secno">4.8.10.10.5 </span>Timed track API</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#cue-events"><span class="secno">4.8.10.10.6 </span>Event definitions</a></li></ol></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#user-interface"><span class="secno">4.8.10.11 </span>User interface</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#time-ranges"><span class="secno">4.8.10.12 </span>Time ranges</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#mediaevents"><span class="secno">4.8.10.13 </span>Event summary</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#security-and-privacy-considerations"><span class="secno">4.8.10.14 </span>Security and privacy considerations</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-canvas-element"><span class="secno">4.8.11 </span>The <code>canvas</code> element</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#color-spaces-and-color-correction"><span class="secno">4.8.11.1 </span>Color spaces and color correction</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#security-with-canvas-elements"><span class="secno">4.8.11.2 </span>Security with <code>canvas</code> elements</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-map-element"><span class="secno">4.8.12 </span>The <code>map</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-area-element"><span class="secno">4.8.13 </span>The <code>area</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#image-maps"><span class="secno">4.8.14 </span>Image maps</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#authoring"><span class="secno">4.8.14.1 </span>Authoring</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#processing-model"><span class="secno">4.8.14.2 </span>Processing model</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#mathml"><span class="secno">4.8.15 </span>MathML</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#svg-0"><span class="secno">4.8.16 </span>SVG</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#dimension-attributes"><span class="secno">4.8.17 </span>Dimension attributes</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#tabular-data"><span class="secno">4.9 </span>Tabular data</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-table-element"><span class="secno">4.9.1 </span>The <code>table</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-caption-element"><span class="secno">4.9.2 </span>The <code>caption</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-colgroup-element"><span class="secno">4.9.3 </span>The <code>colgroup</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-col-element"><span class="secno">4.9.4 </span>The <code>col</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-tbody-element"><span class="secno">4.9.5 </span>The <code>tbody</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-thead-element"><span class="secno">4.9.6 </span>The <code>thead</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-tfoot-element"><span class="secno">4.9.7 </span>The <code>tfoot</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-tr-element"><span class="secno">4.9.8 </span>The <code>tr</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-td-element"><span class="secno">4.9.9 </span>The <code>td</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-th-element"><span class="secno">4.9.10 </span>The <code>th</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#attributes-common-to-td-and-th-elements"><span class="secno">4.9.11 </span>Attributes common to <code>td</code> and <code>th</code> elements</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#processing-model-0"><span class="secno">4.9.12 </span>Processing model</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#forming-a-table"><span class="secno">4.9.12.1 </span>Forming a table</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#header-and-data-cell-semantics"><span class="secno">4.9.12.2 </span>Forming relationships between data cells and header cells</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#examples"><span class="secno">4.9.13 </span>Examples</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#forms"><span class="secno">4.10 </span>Forms</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction-0"><span class="secno">4.10.1 </span>Introduction</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#writing-a-form-s-user-interface"><span class="secno">4.10.1.1 </span>Writing a form's user interface</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#implementing-the-server-side-processing-for-a-form"><span class="secno">4.10.1.2 </span>Implementing the server-side processing for a form</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#configuring-a-form-to-communicate-with-a-server"><span class="secno">4.10.1.3 </span>Configuring a form to communicate with a server</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#client-side-form-validation"><span class="secno">4.10.1.4 </span>Client-side form validation</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#categories"><span class="secno">4.10.2 </span>Categories</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-form-element"><span class="secno">4.10.3 </span>The <code>form</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-fieldset-element"><span class="secno">4.10.4 </span>The <code>fieldset</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-legend-element"><span class="secno">4.10.5 </span>The <code>legend</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-label-element"><span class="secno">4.10.6 </span>The <code>label</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-input-element"><span class="secno">4.10.7 </span>The <code>input</code> element</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#states-of-the-type-attribute"><span class="secno">4.10.7.1 </span>States of the <code title="attr-input-type">type</code> attribute</a>
        <ol>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#hidden-state"><span class="secno">4.10.7.1.1 </span>Hidden state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#text-state-and-search-state"><span class="secno">4.10.7.1.2 </span>Text state and Search state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#telephone-state"><span class="secno">4.10.7.1.3 </span>Telephone state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#url-state"><span class="secno">4.10.7.1.4 </span>URL state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#e-mail-state"><span class="secno">4.10.7.1.5 </span>E-mail state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#password-state"><span class="secno">4.10.7.1.6 </span>Password state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#date-and-time-state"><span class="secno">4.10.7.1.7 </span>Date and Time state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#date-state"><span class="secno">4.10.7.1.8 </span>Date state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#month-state"><span class="secno">4.10.7.1.9 </span>Month state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#week-state"><span class="secno">4.10.7.1.10 </span>Week state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#time-state"><span class="secno">4.10.7.1.11 </span>Time state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#local-date-and-time-state"><span class="secno">4.10.7.1.12 </span>Local Date and Time state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#number-state"><span class="secno">4.10.7.1.13 </span>Number state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#range-state"><span class="secno">4.10.7.1.14 </span>Range state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#color-state"><span class="secno">4.10.7.1.15 </span>Color state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#checkbox-state"><span class="secno">4.10.7.1.16 </span>Checkbox state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#radio-button-state"><span class="secno">4.10.7.1.17 </span>Radio Button state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#file-upload-state"><span class="secno">4.10.7.1.18 </span>File Upload state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#submit-button-state"><span class="secno">4.10.7.1.19 </span>Submit Button state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#image-button-state"><span class="secno">4.10.7.1.20 </span>Image Button state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#reset-button-state"><span class="secno">4.10.7.1.21 </span>Reset Button state</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#button-state"><span class="secno">4.10.7.1.22 </span>Button state</a></li></ol></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#common-input-element-attributes"><span class="secno">4.10.7.2 </span>Common <code>input</code> element attributes</a>
        <ol>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-autocomplete-attribute"><span class="secno">4.10.7.2.1 </span>The <code title="attr-input-autocomplete">autocomplete</code> attribute</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-dirname-attribute"><span class="secno">4.10.7.2.2 </span>The <code title="attr-input-dirname">dirname</code> attribute</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-list-attribute"><span class="secno">4.10.7.2.3 </span>The <code title="attr-input-list">list</code> attribute</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-readonly-attribute"><span class="secno">4.10.7.2.4 </span>The <code title="attr-input-readonly">readonly</code> attribute</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-size-attribute"><span class="secno">4.10.7.2.5 </span>The <code title="attr-input-size">size</code> attribute</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-required-attribute"><span class="secno">4.10.7.2.6 </span>The <code title="attr-input-required">required</code> attribute</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-multiple-attribute"><span class="secno">4.10.7.2.7 </span>The <code title="attr-input-multiple">multiple</code> attribute</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-maxlength-attribute"><span class="secno">4.10.7.2.8 </span>The <code title="attr-input-maxlength">maxlength</code> attribute</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-pattern-attribute"><span class="secno">4.10.7.2.9 </span>The <code title="attr-input-pattern">pattern</code> attribute</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-min-and-max-attributes"><span class="secno">4.10.7.2.10 </span>The <code title="attr-input-min">min</code> and <code title="attr-input-max">max</code> attributes</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-step-attribute"><span class="secno">4.10.7.2.11 </span>The <code title="attr-input-step">step</code> attribute</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-placeholder-attribute"><span class="secno">4.10.7.2.12 </span>The <code title="attr-input-placeholder">placeholder</code> attribute</a></li></ol></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#common-input-element-apis"><span class="secno">4.10.7.3 </span>Common <code>input</code> element APIs</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#common-event-behaviors"><span class="secno">4.10.7.4 </span>Common event behaviors</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-button-element"><span class="secno">4.10.8 </span>The <code>button</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-select-element"><span class="secno">4.10.9 </span>The <code>select</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-datalist-element"><span class="secno">4.10.10 </span>The <code>datalist</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-optgroup-element"><span class="secno">4.10.11 </span>The <code>optgroup</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-option-element"><span class="secno">4.10.12 </span>The <code>option</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-textarea-element"><span class="secno">4.10.13 </span>The <code>textarea</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-keygen-element"><span class="secno">4.10.14 </span>The <code>keygen</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-output-element"><span class="secno">4.10.15 </span>The <code>output</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-progress-element"><span class="secno">4.10.16 </span>The <code>progress</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-meter-element"><span class="secno">4.10.17 </span>The <code>meter</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#association-of-controls-and-forms"><span class="secno">4.10.18 </span>Association of controls and forms</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#attributes-common-to-form-controls"><span class="secno">4.10.19 </span>Attributes common to form controls</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#naming-form-controls"><span class="secno">4.10.19.1 </span>Naming form controls</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#enabling-and-disabling-form-controls"><span class="secno">4.10.19.2 </span>Enabling and disabling form controls</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#a-form-control-s-value"><span class="secno">4.10.19.3 </span>A form control's value</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#autofocusing-a-form-control"><span class="secno">4.10.19.4 </span>Autofocusing a form control</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#limiting-user-input-length"><span class="secno">4.10.19.5 </span>Limiting user input length</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#form-submission-0"><span class="secno">4.10.19.6 </span>Form submission</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#submitting-element-directionality"><span class="secno">4.10.19.7 </span>Submitting element directionality</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#textFieldSelection"><span class="secno">4.10.20 </span>APIs for the text field selections</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#constraints"><span class="secno">4.10.21 </span>Constraints</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#definitions"><span class="secno">4.10.21.1 </span>Definitions</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#constraint-validation"><span class="secno">4.10.21.2 </span>Constraint validation</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-constraint-validation-api"><span class="secno">4.10.21.3 </span>The constraint validation API</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#security-forms"><span class="secno">4.10.21.4 </span>Security</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#form-submission"><span class="secno">4.10.22 </span>Form submission</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction-1"><span class="secno">4.10.22.1 </span>Introduction</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#implicit-submission"><span class="secno">4.10.22.2 </span>Implicit submission</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#form-submission-algorithm"><span class="secno">4.10.22.3 </span>Form submission algorithm</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#url-encoded-form-data"><span class="secno">4.10.22.4 </span>URL-encoded form data</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#multipart-form-data"><span class="secno">4.10.22.5 </span>Multipart form data</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#plain-text-form-data"><span class="secno">4.10.22.6 </span>Plain text form data</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#resetting-a-form"><span class="secno">4.10.23 </span>Resetting a form</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#event-dispatch"><span class="secno">4.10.24 </span>Event dispatch</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#interactive-elements"><span class="secno">4.11 </span>Interactive elements</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-details-element"><span class="secno">4.11.1 </span>The <code>details</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-summary-element"><span class="secno">4.11.2 </span>The <code>summary</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-command"><span class="secno">4.11.3 </span>The <code>command</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#menus"><span class="secno">4.11.4 </span>The <code>menu</code> element</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#menus-intro"><span class="secno">4.11.4.1 </span>Introduction</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#building-menus-and-toolbars"><span class="secno">4.11.4.2 </span>Building menus and toolbars</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#context-menus"><span class="secno">4.11.4.3 </span>Context menus</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#toolbars"><span class="secno">4.11.4.4 </span>Toolbars</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#commands"><span class="secno">4.11.5 </span>Commands</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#using-the-a-element-to-define-a-command"><span class="secno">4.11.5.1 </span>Using the <code>a</code> element to define a command</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#using-the-button-element-to-define-a-command"><span class="secno">4.11.5.2 </span>Using the <code>button</code> element to define a command</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#using-the-input-element-to-define-a-command"><span class="secno">4.11.5.3 </span>Using the <code>input</code> element to define a command</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#using-the-option-element-to-define-a-command"><span class="secno">4.11.5.4 </span>Using the <code>option</code> element to define a command</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#using-the-command-element-to-define-a-command"><span class="secno">4.11.5.5 </span>Using the <code>command</code> element to define
  a command</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#using-the-accesskey-attribute-on-a-label-element-to-define-a-command"><span class="secno">4.11.5.6 </span>Using the <code title="attr-accesskey">accesskey</code> attribute on a <code>label</code> element to define a command</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#using-the-accesskey-attribute-on-a-legend-element-to-define-a-command"><span class="secno">4.11.5.7 </span>Using the <code title="attr-accesskey">accesskey</code> attribute on a <code>legend</code> element to define a command</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#using-the-accesskey-attribute-to-define-a-command-on-other-elements"><span class="secno">4.11.5.8 </span>Using the <code title="attr-accesskey">accesskey</code> attribute to define a command on other elements</a></li></ol></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#links"><span class="secno">4.12 </span>Links</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction-2"><span class="secno">4.12.1 </span>Introduction</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#links-created-by-a-and-area-elements"><span class="secno">4.12.2 </span>Links created by <code>a</code> and <code>area</code> elements</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#following-hyperlinks"><span class="secno">4.12.3 </span>Following hyperlinks</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#linkTypes"><span class="secno">4.12.4 </span>Link types</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rel-alternate"><span class="secno">4.12.4.1 </span>Link type "<code>alternate</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rel-archives"><span class="secno">4.12.4.2 </span>Link type "<code>archives</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-author"><span class="secno">4.12.4.3 </span>Link type "<code>author</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-bookmark"><span class="secno">4.12.4.4 </span>Link type "<code>bookmark</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-external"><span class="secno">4.12.4.5 </span>Link type "<code>external</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-help"><span class="secno">4.12.4.6 </span>Link type "<code>help</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rel-icon"><span class="secno">4.12.4.7 </span>Link type "<code>icon</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-license"><span class="secno">4.12.4.8 </span>Link type "<code>license</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-nofollow"><span class="secno">4.12.4.9 </span>Link type "<code>nofollow</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-noreferrer"><span class="secno">4.12.4.10 </span>Link type "<code>noreferrer</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-pingback"><span class="secno">4.12.4.11 </span>Link type "<code>pingback</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-prefetch"><span class="secno">4.12.4.12 </span>Link type "<code>prefetch</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-search"><span class="secno">4.12.4.13 </span>Link type "<code>search</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-stylesheet"><span class="secno">4.12.4.14 </span>Link type "<code>stylesheet</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-sidebar"><span class="secno">4.12.4.15 </span>Link type "<code>sidebar</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-tag"><span class="secno">4.12.4.16 </span>Link type "<code>tag</code>"</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#hierarchical-link-types"><span class="secno">4.12.4.17 </span>Hierarchical link types</a>
        <ol>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-index"><span class="secno">4.12.4.17.1 </span>Link type "<code>index</code>"</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-up"><span class="secno">4.12.4.17.2 </span>Link type "<code>up</code>"</a></li></ol></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#sequential-link-types"><span class="secno">4.12.4.18 </span>Sequential link types</a>
        <ol>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-first"><span class="secno">4.12.4.18.1 </span>Link type "<code>first</code>"</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-last"><span class="secno">4.12.4.18.2 </span>Link type "<code>last</code>"</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-next"><span class="secno">4.12.4.18.3 </span>Link type "<code>next</code>"</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#link-type-prev"><span class="secno">4.12.4.18.4 </span>Link type "<code>prev</code>"</a></li></ol></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#other-link-types"><span class="secno">4.12.4.19 </span>Other link types</a></li></ol></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#common-idioms-without-dedicated-elements"><span class="secno">4.13 </span>Common idioms without dedicated elements</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-main-part-of-the-content"><span class="secno">4.13.1 </span>The main part of the content</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#tag-clouds"><span class="secno">4.13.2 </span>Tag clouds</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#conversations"><span class="secno">4.13.3 </span>Conversations</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#footnotes"><span class="secno">4.13.4 </span>Footnotes</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#matching-html-elements-using-selectors"><span class="secno">4.14 </span>Matching HTML elements using selectors</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#selectors"><span class="secno">4.14.1 </span>Case-sensitivity</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#pseudo-classes"><span class="secno">4.14.2 </span>Pseudo-classes</a></li></ol></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#browsers"><span class="secno">5 </span>Loading Web pages</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#windows"><span class="secno">5.1 </span>Browsing contexts</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#nested-browsing-contexts"><span class="secno">5.1.1 </span>Nested browsing contexts</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#navigating-nested-browsing-contexts-in-the-dom"><span class="secno">5.1.1.1 </span>Navigating nested browsing contexts in the DOM</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#auxiliary-browsing-contexts"><span class="secno">5.1.2 </span>Auxiliary browsing contexts</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#navigating-auxiliary-browsing-contexts-in-the-dom"><span class="secno">5.1.2.1 </span>Navigating auxiliary browsing contexts in the DOM</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#secondary-browsing-contexts"><span class="secno">5.1.3 </span>Secondary browsing contexts</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#security-nav"><span class="secno">5.1.4 </span>Security</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#groupings-of-browsing-contexts"><span class="secno">5.1.5 </span>Groupings of browsing contexts</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#browsing-context-names"><span class="secno">5.1.6 </span>Browsing context names</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-window-object"><span class="secno">5.2 </span>The <code>Window</code> object</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#security-window"><span class="secno">5.2.1 </span>Security</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#apis-for-creating-and-navigating-browsing-contexts-by-name"><span class="secno">5.2.2 </span>APIs for creating and navigating browsing contexts by name</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#accessing-other-browsing-contexts"><span class="secno">5.2.3 </span>Accessing other browsing contexts</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#named-access-on-the-window-object"><span class="secno">5.2.4 </span>Named access on the <code>Window</code> object</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#garbage-collection-and-browsing-contexts"><span class="secno">5.2.5 </span>Garbage collection and browsing contexts</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#browser-interface-elements"><span class="secno">5.2.6 </span>Browser interface elements</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-windowproxy-object"><span class="secno">5.2.7 </span>The <code>WindowProxy</code> object</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#origin-0"><span class="secno">5.3 </span>Origin</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#relaxing-the-same-origin-restriction"><span class="secno">5.3.1 </span>Relaxing the same-origin restriction</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#history"><span class="secno">5.4 </span>Session history and navigation</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-session-history-of-browsing-contexts"><span class="secno">5.4.1 </span>The session history of browsing contexts</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-history-interface"><span class="secno">5.4.2 </span>The <code>History</code> interface</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-location-interface"><span class="secno">5.4.3 </span>The <code>Location</code> interface</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#security-location"><span class="secno">5.4.3.1 </span>Security</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#history-notes"><span class="secno">5.4.4 </span>Implementation notes for session history</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#browsing-the-web"><span class="secno">5.5 </span>Browsing the Web</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#navigating-across-documents"><span class="secno">5.5.1 </span>Navigating across documents</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#read-html"><span class="secno">5.5.2 </span>Page load processing model for HTML files</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#read-xml"><span class="secno">5.5.3 </span>Page load processing model for XML files</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#read-text"><span class="secno">5.5.4 </span>Page load processing model for text files</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#read-image"><span class="secno">5.5.5 </span>Page load processing model for images</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#read-plugin"><span class="secno">5.5.6 </span>Page load processing model for content that uses plugins</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#read-ua-inline"><span class="secno">5.5.7 </span>Page load processing model for inline content that doesn't have a DOM</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#scroll-to-fragid"><span class="secno">5.5.8 </span>Navigating to a fragment identifier</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#history-traversal"><span class="secno">5.5.9 </span>History traversal</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#event-definitions"><span class="secno">5.5.9.1 </span>Event definitions</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#unloading-documents"><span class="secno">5.5.10 </span>Unloading documents</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#event-definition"><span class="secno">5.5.10.1 </span>Event definition</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#aborting-a-document-load"><span class="secno">5.5.11 </span>Aborting a document load</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#offline"><span class="secno">5.6 </span>Offline Web applications</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction-3"><span class="secno">5.6.1 </span>Introduction</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#appcacheevents"><span class="secno">5.6.1.1 </span>Event summary</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#appcache"><span class="secno">5.6.2 </span>Application caches</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#manifests"><span class="secno">5.6.3 </span>The cache manifest syntax</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#some-sample-manifests"><span class="secno">5.6.3.1 </span>Some sample manifests</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#writing-cache-manifests"><span class="secno">5.6.3.2 </span>Writing cache manifests</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-cache-manifests"><span class="secno">5.6.3.3 </span>Parsing cache manifests</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#downloading-or-updating-an-application-cache"><span class="secno">5.6.4 </span>Downloading or updating an application cache</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-application-cache-selection-algorithm"><span class="secno">5.6.5 </span>The application cache selection algorithm</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#changesToNetworkingModel"><span class="secno">5.6.6 </span>Changes to the networking model</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#expiring-application-caches"><span class="secno">5.6.7 </span>Expiring application caches</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#disk-space"><span class="secno">5.6.8 </span>Disk space</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#application-cache-api"><span class="secno">5.6.9 </span>Application cache API</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#browser-state"><span class="secno">5.6.10 </span>Browser state</a></li></ol></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#webappapis"><span class="secno">6 </span>Web application APIs</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#scripting"><span class="secno">6.1 </span>Scripting</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction-4"><span class="secno">6.1.1 </span>Introduction</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#enabling-and-disabling-scripting"><span class="secno">6.1.2 </span>Enabling and disabling scripting</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#processing-model-1"><span class="secno">6.1.3 </span>Processing model</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#definitions-0"><span class="secno">6.1.3.1 </span>Definitions</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#calling-scripts"><span class="secno">6.1.3.2 </span>Calling scripts</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#creating-scripts"><span class="secno">6.1.3.3 </span>Creating scripts</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#killing-scripts"><span class="secno">6.1.3.4 </span>Killing scripts</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#event-loops"><span class="secno">6.1.4 </span>Event loops</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#definitions-1"><span class="secno">6.1.4.1 </span>Definitions</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#processing-model-2"><span class="secno">6.1.4.2 </span>Processing model</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#generic-task-sources"><span class="secno">6.1.4.3 </span>Generic task sources</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#javascript-protocol"><span class="secno">6.1.5 </span>The <code title="">javascript:</code> protocol</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#events"><span class="secno">6.1.6 </span>Events</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#event-handler-attributes"><span class="secno">6.1.6.1 </span>Event handlers</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#event-handlers-on-elements-document-objects-and-window-objects"><span class="secno">6.1.6.2 </span>Event handlers on elements, <code>Document</code> objects, and <code>Window</code> objects</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#event-firing"><span class="secno">6.1.6.3 </span>Event firing</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#events-and-the-window-object"><span class="secno">6.1.6.4 </span>Events and the <code>Window</code> object</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#runtime-script-errors"><span class="secno">6.1.6.5 </span>Runtime script errors</a></li></ol></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#timers"><span class="secno">6.2 </span>Timers</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#user-prompts"><span class="secno">6.3 </span>User prompts</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#simple-dialogs"><span class="secno">6.3.1 </span>Simple dialogs</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#printing"><span class="secno">6.3.2 </span>Printing</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#dialogs-implemented-using-separate-documents"><span class="secno">6.3.3 </span>Dialogs implemented using separate documents</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#system-state-and-capabilities:-the-navigator-object"><span class="secno">6.4 </span>System state and capabilities: the <code>Navigator</code> object</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#client-identification"><span class="secno">6.4.1 </span>Client identification</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#custom-handlers"><span class="secno">6.4.2 </span>Custom scheme and content handlers</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#security-and-privacy"><span class="secno">6.4.2.1 </span>Security and privacy</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#sample-handler-impl"><span class="secno">6.4.2.2 </span>Sample user interface</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#manually-releasing-the-storage-mutex"><span class="secno">6.4.3 </span>Manually releasing the storage mutex</a></li></ol></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#editing"><span class="secno">7 </span>User interaction</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-hidden-attribute"><span class="secno">7.1 </span>The <code>hidden</code> attribute</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#activation"><span class="secno">7.2 </span>Activation</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#focus"><span class="secno">7.3 </span>Focus</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#sequential-focus-navigation-and-the-tabindex-attribute"><span class="secno">7.3.1 </span>Sequential focus navigation and the <code title="attr-tabindex">tabindex</code> attribute</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#focus-management"><span class="secno">7.3.2 </span>Focus management</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#document-level-focus-apis"><span class="secno">7.3.3 </span>Document-level focus APIs</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#element-level-focus-apis"><span class="secno">7.3.4 </span>Element-level focus APIs</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#assigning-keyboard-shortcuts"><span class="secno">7.4 </span>Assigning keyboard shortcuts</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction-5"><span class="secno">7.4.1 </span>Introduction</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-accesskey-attribute"><span class="secno">7.4.2 </span>The <code>accesskey</code> attribute</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#processing-model-3"><span class="secno">7.4.3 </span>Processing model</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#contenteditable"><span class="secno">7.5 </span>The <code title="attr-contenteditable">contenteditable</code> attribute</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#user-editing-actions"><span class="secno">7.5.1 </span>User editing actions</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#making-entire-documents-editable"><span class="secno">7.5.2 </span>Making entire documents editable</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#spelling-and-grammar-checking"><span class="secno">7.6 </span>Spelling and grammar checking</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#dnd"><span class="secno">7.7 </span>Drag and drop</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction-6"><span class="secno">7.7.1 </span>Introduction</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-drag-data-store"><span class="secno">7.7.2 </span>The drag data store</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-datatransfer-interface"><span class="secno">7.7.3 </span>The <code>DataTransfer</code> interface</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-datatransferitems-interface"><span class="secno">7.7.3.1 </span>The <code>DataTransferItems</code> interface</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-datatransferitem-interface"><span class="secno">7.7.3.2 </span>The <code>DataTransferItem</code> interface</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-dragevent-interface"><span class="secno">7.7.4 </span>The <code>DragEvent</code> interface</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#drag-and-drop-processing-model"><span class="secno">7.7.5 </span>Drag-and-drop processing model</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#dndevents"><span class="secno">7.7.6 </span>Events summary</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-draggable-attribute"><span class="secno">7.7.7 </span>The <code>draggable</code> attribute</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-dropzone-attribute"><span class="secno">7.7.8 </span>The <code>dropzone</code> attribute</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#security-risks-in-the-drag-and-drop-model"><span class="secno">7.7.9 </span>Security risks in the drag-and-drop model</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#undo"><span class="secno">7.8 </span>Undo history</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#definitions-2"><span class="secno">7.8.1 </span>Definitions</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-undomanager-interface"><span class="secno">7.8.2 </span>The <code>UndoManager</code> interface</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#undo:-moving-back-in-the-undo-transaction-history"><span class="secno">7.8.3 </span>Undo: moving back in the undo transaction history</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#redo:-moving-forward-in-the-undo-transaction-history"><span class="secno">7.8.4 </span>Redo: moving forward in the undo transaction history</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-undomanagerevent-interface-and-the-undo-and-redo-events"><span class="secno">7.8.5 </span>The <code>UndoManagerEvent</code> interface and the <code title="event-undo">undo</code> and <code title="event-redo">redo</code> events</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#implementation-notes"><span class="secno">7.8.6 </span>Implementation notes</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#editing-apis"><span class="secno">7.9 </span>Editing APIs</a></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#syntax"><span class="secno">8 </span>The HTML syntax</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#writing"><span class="secno">8.1 </span>Writing HTML documents</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-doctype"><span class="secno">8.1.1 </span>The DOCTYPE</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#elements-0"><span class="secno">8.1.2 </span>Elements</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#start-tags"><span class="secno">8.1.2.1 </span>Start tags</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#end-tags"><span class="secno">8.1.2.2 </span>End tags</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#attributes-0"><span class="secno">8.1.2.3 </span>Attributes</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#optional-tags"><span class="secno">8.1.2.4 </span>Optional tags</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#element-restrictions"><span class="secno">8.1.2.5 </span>Restrictions on content models</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#cdata-rcdata-restrictions"><span class="secno">8.1.2.6 </span>Restrictions on the contents of raw text and RCDATA elements</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#text-0"><span class="secno">8.1.3 </span>Text</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#newlines"><span class="secno">8.1.3.1 </span>Newlines</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#character-references"><span class="secno">8.1.4 </span>Character references</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#cdata-sections"><span class="secno">8.1.5 </span>CDATA sections</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#comments"><span class="secno">8.1.6 </span>Comments</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing"><span class="secno">8.2 </span>Parsing HTML documents</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#overview-of-the-parsing-model"><span class="secno">8.2.1 </span>Overview of the parsing model</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-input-stream"><span class="secno">8.2.2 </span>The input stream</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#determining-the-character-encoding"><span class="secno">8.2.2.1 </span>Determining the character encoding</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#character-encodings-0"><span class="secno">8.2.2.2 </span>Character encodings</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#preprocessing-the-input-stream"><span class="secno">8.2.2.3 </span>Preprocessing the input stream</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#changing-the-encoding-while-parsing"><span class="secno">8.2.2.4 </span>Changing the encoding while parsing</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#parse-state"><span class="secno">8.2.3 </span>Parse state</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-insertion-mode"><span class="secno">8.2.3.1 </span>The insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-stack-of-open-elements"><span class="secno">8.2.3.2 </span>The stack of open elements</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-list-of-active-formatting-elements"><span class="secno">8.2.3.3 </span>The list of active formatting elements</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-element-pointers"><span class="secno">8.2.3.4 </span>The element pointers</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#other-parsing-state-flags"><span class="secno">8.2.3.5 </span>Other parsing state flags</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#tokenization"><span class="secno">8.2.4 </span>Tokenization</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#data-state"><span class="secno">8.2.4.1 </span>Data state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#character-reference-in-data-state"><span class="secno">8.2.4.2 </span>Character reference in data state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rcdata-state"><span class="secno">8.2.4.3 </span>RCDATA state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#character-reference-in-rcdata-state"><span class="secno">8.2.4.4 </span>Character reference in RCDATA state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rawtext-state"><span class="secno">8.2.4.5 </span>RAWTEXT state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-state"><span class="secno">8.2.4.6 </span>Script data state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#plaintext-state"><span class="secno">8.2.4.7 </span>PLAINTEXT state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#tag-open-state"><span class="secno">8.2.4.8 </span>Tag open state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#end-tag-open-state"><span class="secno">8.2.4.9 </span>End tag open state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#tag-name-state"><span class="secno">8.2.4.10 </span>Tag name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rcdata-less-than-sign-state"><span class="secno">8.2.4.11 </span>RCDATA less-than sign state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rcdata-end-tag-open-state"><span class="secno">8.2.4.12 </span>RCDATA end tag open state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rcdata-end-tag-name-state"><span class="secno">8.2.4.13 </span>RCDATA end tag name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rawtext-less-than-sign-state"><span class="secno">8.2.4.14 </span>RAWTEXT less-than sign state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rawtext-end-tag-open-state"><span class="secno">8.2.4.15 </span>RAWTEXT end tag open state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#rawtext-end-tag-name-state"><span class="secno">8.2.4.16 </span>RAWTEXT end tag name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-less-than-sign-state"><span class="secno">8.2.4.17 </span>Script data less-than sign state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-end-tag-open-state"><span class="secno">8.2.4.18 </span>Script data end tag open state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-end-tag-name-state"><span class="secno">8.2.4.19 </span>Script data end tag name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-escape-start-state"><span class="secno">8.2.4.20 </span>Script data escape start state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-escape-start-dash-state"><span class="secno">8.2.4.21 </span>Script data escape start dash state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-escaped-state"><span class="secno">8.2.4.22 </span>Script data escaped state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-escaped-dash-state"><span class="secno">8.2.4.23 </span>Script data escaped dash state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-escaped-dash-dash-state"><span class="secno">8.2.4.24 </span>Script data escaped dash dash state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-escaped-less-than-sign-state"><span class="secno">8.2.4.25 </span>Script data escaped less-than sign state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-escaped-end-tag-open-state"><span class="secno">8.2.4.26 </span>Script data escaped end tag open state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-escaped-end-tag-name-state"><span class="secno">8.2.4.27 </span>Script data escaped end tag name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-double-escape-start-state"><span class="secno">8.2.4.28 </span>Script data double escape start state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-double-escaped-state"><span class="secno">8.2.4.29 </span>Script data double escaped state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-double-escaped-dash-state"><span class="secno">8.2.4.30 </span>Script data double escaped dash state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-double-escaped-dash-dash-state"><span class="secno">8.2.4.31 </span>Script data double escaped dash dash state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-double-escaped-less-than-sign-state"><span class="secno">8.2.4.32 </span>Script data double escaped less-than sign state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#script-data-double-escape-end-state"><span class="secno">8.2.4.33 </span>Script data double escape end state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#before-attribute-name-state"><span class="secno">8.2.4.34 </span>Before attribute name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#attribute-name-state"><span class="secno">8.2.4.35 </span>Attribute name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#after-attribute-name-state"><span class="secno">8.2.4.36 </span>After attribute name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#before-attribute-value-state"><span class="secno">8.2.4.37 </span>Before attribute value state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#attribute-value-double-quoted-state"><span class="secno">8.2.4.38 </span>Attribute value (double-quoted) state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#attribute-value-single-quoted-state"><span class="secno">8.2.4.39 </span>Attribute value (single-quoted) state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#attribute-value-unquoted-state"><span class="secno">8.2.4.40 </span>Attribute value (unquoted) state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#character-reference-in-attribute-value-state"><span class="secno">8.2.4.41 </span>Character reference in attribute value state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#after-attribute-value-quoted-state"><span class="secno">8.2.4.42 </span>After attribute value (quoted) state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#self-closing-start-tag-state"><span class="secno">8.2.4.43 </span>Self-closing start tag state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#bogus-comment-state"><span class="secno">8.2.4.44 </span>Bogus comment state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#markup-declaration-open-state"><span class="secno">8.2.4.45 </span>Markup declaration open state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#comment-start-state"><span class="secno">8.2.4.46 </span>Comment start state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#comment-start-dash-state"><span class="secno">8.2.4.47 </span>Comment start dash state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#comment-state"><span class="secno">8.2.4.48 </span>Comment state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#comment-end-dash-state"><span class="secno">8.2.4.49 </span>Comment end dash state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#comment-end-state"><span class="secno">8.2.4.50 </span>Comment end state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#comment-end-bang-state"><span class="secno">8.2.4.51 </span>Comment end bang state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#doctype-state"><span class="secno">8.2.4.52 </span>DOCTYPE state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#before-doctype-name-state"><span class="secno">8.2.4.53 </span>Before DOCTYPE name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#doctype-name-state"><span class="secno">8.2.4.54 </span>DOCTYPE name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#after-doctype-name-state"><span class="secno">8.2.4.55 </span>After DOCTYPE name state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#after-doctype-public-keyword-state"><span class="secno">8.2.4.56 </span>After DOCTYPE public keyword state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#before-doctype-public-identifier-state"><span class="secno">8.2.4.57 </span>Before DOCTYPE public identifier state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#doctype-public-identifier-double-quoted-state"><span class="secno">8.2.4.58 </span>DOCTYPE public identifier (double-quoted) state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#doctype-public-identifier-single-quoted-state"><span class="secno">8.2.4.59 </span>DOCTYPE public identifier (single-quoted) state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#after-doctype-public-identifier-state"><span class="secno">8.2.4.60 </span>After DOCTYPE public identifier state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#between-doctype-public-and-system-identifiers-state"><span class="secno">8.2.4.61 </span>Between DOCTYPE public and system identifiers state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#after-doctype-system-keyword-state"><span class="secno">8.2.4.62 </span>After DOCTYPE system keyword state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#before-doctype-system-identifier-state"><span class="secno">8.2.4.63 </span>Before DOCTYPE system identifier state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#doctype-system-identifier-double-quoted-state"><span class="secno">8.2.4.64 </span>DOCTYPE system identifier (double-quoted) state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#doctype-system-identifier-single-quoted-state"><span class="secno">8.2.4.65 </span>DOCTYPE system identifier (single-quoted) state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#after-doctype-system-identifier-state"><span class="secno">8.2.4.66 </span>After DOCTYPE system identifier state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#bogus-doctype-state"><span class="secno">8.2.4.67 </span>Bogus DOCTYPE state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#cdata-section-state"><span class="secno">8.2.4.68 </span>CDATA section state</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#tokenizing-character-references"><span class="secno">8.2.4.69 </span>Tokenizing character references</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#tree-construction"><span class="secno">8.2.5 </span>Tree construction</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#creating-and-inserting-elements"><span class="secno">8.2.5.1 </span>Creating and inserting elements</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#closing-elements-that-have-implied-end-tags"><span class="secno">8.2.5.2 </span>Closing elements that have implied end tags</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#foster-parenting"><span class="secno">8.2.5.3 </span>Foster parenting</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-initial-insertion-mode"><span class="secno">8.2.5.4 </span>The "initial" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-before-html-insertion-mode"><span class="secno">8.2.5.5 </span>The "before html" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-before-head-insertion-mode"><span class="secno">8.2.5.6 </span>The "before head" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-inhead"><span class="secno">8.2.5.7 </span>The "in head" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-inheadnoscript"><span class="secno">8.2.5.8 </span>The "in head noscript" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-after-head-insertion-mode"><span class="secno">8.2.5.9 </span>The "after head" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-inbody"><span class="secno">8.2.5.10 </span>The "in body" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-incdata"><span class="secno">8.2.5.11 </span>The "text" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-intable"><span class="secno">8.2.5.12 </span>The "in table" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-intabletext"><span class="secno">8.2.5.13 </span>The "in table text" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-incaption"><span class="secno">8.2.5.14 </span>The "in caption" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-incolgroup"><span class="secno">8.2.5.15 </span>The "in column group" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-intbody"><span class="secno">8.2.5.16 </span>The "in table body" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-intr"><span class="secno">8.2.5.17 </span>The "in row" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-intd"><span class="secno">8.2.5.18 </span>The "in cell" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-inselect"><span class="secno">8.2.5.19 </span>The "in select" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-inselectintable"><span class="secno">8.2.5.20 </span>The "in select in table" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-inforeign"><span class="secno">8.2.5.21 </span>The "in foreign content" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-afterbody"><span class="secno">8.2.5.22 </span>The "after body" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-inframeset"><span class="secno">8.2.5.23 </span>The "in frameset" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-main-afterframeset"><span class="secno">8.2.5.24 </span>The "after frameset" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-after-after-body-insertion-mode"><span class="secno">8.2.5.25 </span>The "after after body" insertion mode</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-after-after-frameset-insertion-mode"><span class="secno">8.2.5.26 </span>The "after after frameset" insertion mode</a></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-end"><span class="secno">8.2.6 </span>The end</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#coercing-an-html-dom-into-an-infoset"><span class="secno">8.2.7 </span>Coercing an HTML DOM into an infoset</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#an-introduction-to-error-handling-and-strange-cases-in-the-parser"><span class="secno">8.2.8 </span>An introduction to error handling and strange cases in the parser</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#misnested-tags:-b-i-b-i"><span class="secno">8.2.8.1 </span>Misnested tags: &lt;b&gt;&lt;i&gt;&lt;/b&gt;&lt;/i&gt;</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#misnested-tags:-b-p-b-p"><span class="secno">8.2.8.2 </span>Misnested tags: &lt;b&gt;&lt;p&gt;&lt;/b&gt;&lt;/p&gt;</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#unexpected-markup-in-tables"><span class="secno">8.2.8.3 </span>Unexpected markup in tables</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#scripts-that-modify-the-page-as-it-is-being-parsed"><span class="secno">8.2.8.4 </span>Scripts that modify the page as it is being parsed</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#unclosed-formatting-elements"><span class="secno">8.2.8.5 </span>Unclosed formatting elements</a></li></ol></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#serializing-html-fragments"><span class="secno">8.3 </span>Serializing HTML fragments</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-html-fragments"><span class="secno">8.4 </span>Parsing HTML fragments</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#named-character-references"><span class="secno">8.5 </span>Named character references</a></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-xhtml-syntax"><span class="secno">9 </span>The XHTML syntax</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#writing-xhtml-documents"><span class="secno">9.1 </span>Writing XHTML documents</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-xhtml-documents"><span class="secno">9.2 </span>Parsing XHTML documents</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#serializing-xhtml-fragments"><span class="secno">9.3 </span>Serializing XHTML fragments</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#parsing-xhtml-fragments"><span class="secno">9.4 </span>Parsing XHTML fragments</a></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#rendering"><span class="secno">10 </span>Rendering</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction-7"><span class="secno">10.1 </span>Introduction</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-css-user-agent-style-sheet-and-presentational-hints"><span class="secno">10.2 </span>The CSS user agent style sheet and presentational hints</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction-8"><span class="secno">10.2.1 </span>Introduction</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#display-types"><span class="secno">10.2.2 </span>Display types</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#margins-and-padding"><span class="secno">10.2.3 </span>Margins and padding</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#alignment"><span class="secno">10.2.4 </span>Alignment</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#fonts-and-colors"><span class="secno">10.2.5 </span>Fonts and colors</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#punctuation-and-decorations"><span class="secno">10.2.6 </span>Punctuation and decorations</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#resetting-rules-for-inherited-properties"><span class="secno">10.2.7 </span>Resetting rules for inherited properties</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-hr-element-0"><span class="secno">10.2.8 </span>The <code>hr</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-fieldset-element-0"><span class="secno">10.2.9 </span>The <code>fieldset</code> element</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#replaced-elements"><span class="secno">10.3 </span>Replaced elements</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#embedded-content-2"><span class="secno">10.3.1 </span>Embedded content</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#timed-tracks-0"><span class="secno">10.3.2 </span>Timed tracks</a>
      <ol>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#websrt-cue-text-rendering-rules"><span class="secno">10.3.2.1 </span>WebSRT cue text rendering rules</a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#applying-css-properties-to-websrt-node-objects"><span class="secno">10.3.2.2 </span>Applying CSS properties to <span title="WebSRT Node Object">WebSRT Node Objects</span></a></li>
       <li><a href="http://dev.w3.org/html5/spec/Overview.html#css-extensions"><span class="secno">10.3.2.3 </span>CSS extensions</a>
        <ol>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-::cue-pseudo-element"><span class="secno">10.3.2.3.1 </span>The '::cue' pseudo-element</a></li>
         <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-::cue-part-pseudo-element"><span class="secno">10.3.2.3.2 </span>The '::cue-part' pseudo-element</a></li></ol></li></ol></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#images"><span class="secno">10.3.3 </span>Images</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#attributes-for-embedded-content-and-images"><span class="secno">10.3.4 </span>Attributes for embedded content and images</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#image-maps-0"><span class="secno">10.3.5 </span>Image maps</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#toolbars-0"><span class="secno">10.3.6 </span>Toolbars</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#bindings"><span class="secno">10.4 </span>Bindings</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#introduction-9"><span class="secno">10.4.1 </span>Introduction</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-button-element-0"><span class="secno">10.4.2 </span>The <code>button</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-details-element-0"><span class="secno">10.4.3 </span>The <code>details</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-input-element-as-a-text-entry-widget"><span class="secno">10.4.4 </span>The <code>input</code> element as a text entry widget</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-input-element-as-domain-specific-widgets"><span class="secno">10.4.5 </span>The <code>input</code> element as domain-specific widgets</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-input-element-as-a-range-control"><span class="secno">10.4.6 </span>The <code>input</code> element as a range control</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-input-element-as-a-color-well"><span class="secno">10.4.7 </span>The <code>input</code> element as a color well</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-input-element-as-a-check-box-and-radio-button-widgets"><span class="secno">10.4.8 </span>The <code>input</code> element as a check box and radio button widgets</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-input-element-as-a-file-upload-control"><span class="secno">10.4.9 </span>The <code>input</code> element as a file upload control</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-input-element-as-a-button"><span class="secno">10.4.10 </span>The <code>input</code> element as a button</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-marquee-element-0"><span class="secno">10.4.11 </span>The <code>marquee</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-meter-element-0"><span class="secno">10.4.12 </span>The <code>meter</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-progress-element-0"><span class="secno">10.4.13 </span>The <code>progress</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-select-element-0"><span class="secno">10.4.14 </span>The <code>select</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-textarea-element-0"><span class="secno">10.4.15 </span>The <code>textarea</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-keygen-element-0"><span class="secno">10.4.16 </span>The <code>keygen</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-time-element-0"><span class="secno">10.4.17 </span>The <code>time</code> element</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#frames-and-framesets"><span class="secno">10.5 </span>Frames and framesets</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#interactive-media"><span class="secno">10.6 </span>Interactive media</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#links-forms-and-navigation"><span class="secno">10.6.1 </span>Links, forms, and navigation</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-title-attribute-0"><span class="secno">10.6.2 </span>The <code title="attr-title">title</code> attribute</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#editing-hosts"><span class="secno">10.6.3 </span>Editing hosts</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#text-rendered-in-native-user-interfaces"><span class="secno">10.6.4 </span>Text rendered in native user interfaces</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#print-media"><span class="secno">10.7 </span>Print media</a></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#obsolete"><span class="secno">11 </span>Obsolete features</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#obsolete-but-conforming-features"><span class="secno">11.1 </span>Obsolete but conforming features</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#warnings-for-obsolete-but-conforming-features"><span class="secno">11.1.1 </span>Warnings for obsolete but conforming features</a></li></ol></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#non-conforming-features"><span class="secno">11.2 </span>Non-conforming features</a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#requirements-for-implementations"><span class="secno">11.3 </span>Requirements for implementations</a>
    <ol>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-applet-element"><span class="secno">11.3.1 </span>The <code>applet</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#the-marquee-element"><span class="secno">11.3.2 </span>The <code>marquee</code> element</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#frames"><span class="secno">11.3.3 </span>Frames</a></li>
     <li><a href="http://dev.w3.org/html5/spec/Overview.html#other-elements-attributes-and-apis"><span class="secno">11.3.4 </span>Other elements, attributes and APIs</a></li></ol></li></ol></li>
 <li><a href="http://dev.w3.org/html5/spec/Overview.html#iana"><span class="secno">12 </span>IANA considerations</a>
  <ol>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#text-html"><span class="secno">12.1 </span><code>text/html</code></a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#text-html-sandboxed"><span class="secno">12.2 </span><code>text/html-sandboxed</code></a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#application-xhtml-xml"><span class="secno">12.3 </span><code>application/xhtml+xml</code></a></li>
   <li><a href="http://dev.w3.org/html5/spec/Overview.html#text-cache-manifest"><span class="secno">12.4 </span><code>text/cache-manifest</code></a></li></ol></li>
 <li><a class="no-num" href="http://dev.w3.org/html5/spec/Overview.html#index">Index</a>
  <ol>
   <li><a class="no-num" href="http://dev.w3.org/html5/spec/Overview.html#elements-1">Elements</a></li>
   <li><a class="no-num" href="http://dev.w3.org/html5/spec/Overview.html#element-content-categories">Element content categories</a></li>
   <li><a class="no-num" href="http://dev.w3.org/html5/spec/Overview.html#attributes-1">Attributes</a></li>
   <li><a class="no-num" href="http://dev.w3.org/html5/spec/Overview.html#interfaces">Interfaces</a></li>
   <li><a class="no-num" href="http://dev.w3.org/html5/spec/Overview.html#events-0">Events</a></li></ol></li>
 <li><a class="no-num" href="http://dev.w3.org/html5/spec/Overview.html#references">References</a></li>
 <li><a class="no-num" href="http://dev.w3.org/html5/spec/Overview.html#acknowledgements">Acknowledgements</a></li></ol>
<!--end-toc--><hr><h2 id="introduction"><span class="secno">1 </span>Introduction</h2><h3 id="background"><span class="secno">1.1 </span>Background</h3><p><i>This section is non-normative.</i></p><p>The World Wide Web's markup language has always been HTML. HTML
  was primarily designed as a language for semantically describing
  scientific documents, although its general design and adaptations
  over the years have enabled it to be used to describe a number of
  other types of documents.</p><p>The main area that has not been adequately addressed by HTML is a
  vague subject referred to as Web Applications. This specification
  attempts to rectify this, while at the same time updating the HTML
  specifications to address issues raised in the past few years.</p><h3 id="audience"><span class="secno">1.2 </span>Audience</h3><p><i>This section is non-normative.</i></p><p>This specification is intended for authors of documents and
  scripts that use the features defined in this specification<span class="impl">, implementors of tools that operate on pages that use
  the features defined in this specification, and individuals wishing
  to establish the correctness of documents or implementations with
  respect to the requirements of this specification</span>.</p><p>This document is probably not suited to readers who do not
  already have at least a passing familiarity with Web technologies,
  as in places it sacrifices clarity for precision, and brevity for
  completeness. More approachable tutorials and authoring guides can
  provide a gentler introduction to the topic.</p><p>In particular, familiarity with the basics of DOM Core and DOM
  Events is necessary for a complete understanding of some of the more
  technical parts of this specification. An understanding of Web IDL,
  HTTP, XML, Unicode, character encodings, JavaScript, and CSS will
  also be helpful in places but is not essential.</p><h3 id="scope"><span class="secno">1.3 </span>Scope</h3><p><i>This section is non-normative.</i></p><p>This specification is limited to providing a semantic-level
  markup language and associated semantic-level scripting APIs for
  authoring accessible pages on the Web ranging from static documents
  to dynamic applications.</p><p>The scope of this specification does not include providing
  mechanisms for media-specific customization of presentation
  (although default rendering rules for Web browsers are included at
  the end of this specification, and several mechanisms for hooking
  into CSS are provided as part of the language).</p><p>The scope of this specification is not to describe an entire
  operating system. In particular, hardware configuration software,
  image manipulation tools, and applications that users would be
  expected to use with high-end workstations on a daily basis are out
  of scope. In terms of applications, this specification is targeted
  specifically at applications that would be expected to be used by
  users on an occasional basis, or regularly but from disparate
  locations, with low CPU requirements. For instance online purchasing
  systems, searching systems, games (especially multiplayer online
  games), public telephone books or address books, communications
  software (e-mail clients, instant messaging clients, discussion
  software), document editing software, etc.</p><h3 id="history-1"><span class="secno">1.4 </span>History</h3><p><i>This section is non-normative.</i></p><p>For its first five years (1990-1995), HTML went through a number
  of revisions and experienced a number of extensions, primarily
  hosted first at CERN, and then at the IETF.</p><p>With the creation of the W3C, HTML's development changed venue
  again. A first abortive attempt at extending HTML in 1995 known as
  HTML 3.0 then made way to a more pragmatic approach known as HTML
  3.2, which was completed in 1997. HTML4 followed, reaching
  completion in 1998.</p><p>At this time, the W3C membership decided to stop evolving HTML
  and instead begin work on an XML-based equivalent, called
  XHTML. This effort started with a reformulation of HTML4 in XML,
  known as XHTML 1.0, which added no new features except the new
  serialization, and which was completed in 2000. After XHTML 1.0, the
  W3C's focus turned to making it easier for other working groups to
  extend XHTML, under the banner of XHTML Modularization. In parallel
  with this, the W3C also worked on a new language that was not
  compatible with the earlier HTML and XHTML languages, calling it
  XHTML2.</p><p>Around the time that HTML's evolution was stopped in 1998, parts
  of the API for HTML developed by browser vendors were specified and
  published under the name DOM Level 1 (in 1998) and DOM Level 2 Core
  and DOM Level 2 HTML (starting in 2000 and culminating in
  2003). These efforts then petered out, with some DOM Level 3
  specifications published in 2004 but the working group being closed
  before all the Level 3 drafts were completed.</p><p>In 2003, the publication of XForms, a technology which was
  positioned as the next generation of Web forms, sparked a renewed
  interest in evolving HTML itself, rather than finding replacements
  for it. This interest was borne from the realization that XML's
  deployment as a Web technology was limited to entirely new
  technologies (like RSS and later Atom), rather than as a replacement
  for existing deployed technologies (like HTML).</p><p>A proof of concept to show that it was possible to extend HTML4's
  forms to provide many of the features that XForms 1.0 introduced,
  without requiring browsers to implement rendering engines that were
  incompatible with existing HTML Web pages, was the first result of
  this renewed interest. At this early stage, while the draft was
  already publicly available, and input was already being solicited
  from all sources, the specification was only under Opera Software's
  copyright.</p><p>The idea that HTML's evolution should be reopened was tested at a
  W3C workshop in 2004, where some of the principles that underlie the
  HTML5 work (described below), as well as the aforementioned early
  draft proposal covering just forms-related features, were presented
  to the W3C jointly by Mozilla and Opera. The proposal was rejected
  on the grounds that the proposal conflicted with the previously
  chosen direction for the Web's evolution; the W3C staff and
  membership voted to continue developing XML-based replacements
  instead.</p><p>Shortly thereafter, Apple, Mozilla, and Opera jointly announced
  their intent to continue working on the effort under the umbrella of
  a new venue called the WHATWG. A public mailing list was created,
  and the draft was moved to the WHATWG site. The copyright was
  subsequently amended to be jointly owned by all three vendors, and
  to allow reuse of the specification.</p><p>The WHATWG was based on several core principles, in particular
  that technologies need to be backwards compatible, that
  specifications and implementations need to match even if this means
  changing the specification rather than the implementations, and that
  specifications need to be detailed enough that implementations can
  achieve complete interoperability without reverse-engineering each
  other.</p><p>The latter requirement in particular required that the scope of
  the HTML5 specification include what had previously been specified
  in three separate documents: HTML4, XHTML1, and DOM2 HTML. It also
  meant including significantly more detail than had previously been
  considered the norm.</p><p>In 2006, the W3C indicated an interest to participate in the
  development of HTML5 after all, and in 2007 formed a working group
  chartered to work with the WHATWG on the development of the HTML5
  specification. Apple, Mozilla, and Opera allowed the W3C to publish
  the specification under the W3C copyright, while keeping a version
  with the less restrictive license on the WHATWG site.</p><p>Since then, both groups have been working together.</p><!--w3c-html--><!--VERSION--><p>The <a href="http://www.whatwg.org/specs/web-apps/current-work/">HTML
  specification</a> published by the WHATWG is not identical to
  this specification. At the time of this publication, the main
  differences were that the WHATWG version included features not
  included in this W3C version: some features have been omitted, but
  may be considered for future revisions of HTML beyond HTML5; and
  other features were omitted because at the W3C they are published as
  separate specifications.</p><!--w3c-html--><!--VERSION--><p>A separate document has been published by the W3C HTML working
  group to document the differences between this specification and the
  language described in the HTML4 specification. <a href="http://dev.w3.org/html5/spec/Overview.html#refsHTMLDIFF">[HTMLDIFF]</a></p><h3 id="design-notes"><span class="secno">1.5 </span>Design notes</h3><p><i>This section is non-normative.</i></p><p>It must be admitted that many aspects of HTML appear at first
  glance to be nonsensical and inconsistent.</p><p>HTML, its supporting DOM APIs, as well as many of its supporting
  technologies, have been developed over a period of several decades
  by a wide array of people with different priorities who, in many
  cases, did not know of each other's existence.</p><p>Features have thus arisen from many sources, and have not always
  been designed in especially consistent ways. Furthermore, because of
  the unique characteristics of the Web, implementation bugs have
  often become de-facto, and now de-jure, standards, as content is
  often unintentionally written in ways that rely on them before they
  can be fixed.</p><p>Despite all this, efforts have been made to adhere to certain
  design goals. These are described in the next few subsections.</p><h4 id="serializability-of-script-execution"><span class="secno">1.5.1 </span>Serializability of script execution</h4><p><i>This section is non-normative.</i></p><p>To avoid exposing Web authors to the complexities of
  multithreading, the HTML and DOM APIs are designed such that no
  script can ever detect the simultaneous execution of other
  scripts. Even with <span title="Worker">workers</span>, the intent
  is that the behavior of implementations can be thought of as
  completely serializing the execution of all scripts in all <a href="http://dev.w3.org/html5/spec/Overview.html#browsing-context" title="browsing context">browsing contexts</a>.</p><p class="note">The <code title="dom-navigator-yieldForStorageUpdates"><a href="http://dev.w3.org/html5/spec/Overview.html#dom-navigator-yieldforstorageupdates">navigator.yieldForStorageUpdates()</a></code>
  method, in this model, is equivalent to allowing other scripts to
  run while the calling script is blocked.</p><h4 id="compliance-with-other-specifications"><span class="secno">1.5.2 </span>Compliance with other specifications</h4><p><i>This section is non-normative.</i></p><p>This specification interacts with and relies on a wide variety of
  other specifications. In certain circumstances, unfortunately,
  conflicting needs have led to this specification violating the
  requirements of these other specifications. Whenever this has
  occurred, the transgressions have each been noted as a "<dfn id="willful-violation">willful
  violation</dfn>", and the reason for the violation has been
  noted.</p><h3 id="html-vs-xhtml"><span class="secno">1.6 </span>HTML vs XHTML</h3><p><i>This section is non-normative.</i></p><p>This specification defines an abstract language for describing
  documents and applications, and some APIs for interacting with
  in-memory representations of resources that use this language.</p><p>The in-memory representation is known as "DOM HTML", or "the DOM"
  for short. This specification defines version 5 of DOM HTML, known
  as "DOM5 HTML".</p><p>There are various concrete syntaxes that can be used to transmit
  resources that use this abstract language, two of which are defined
  in this specification.</p><p>The first such concrete syntax is the HTML syntax. This is the
  format suggested for most authors. It is compatible with most legacy
  Web browsers. If a document is transmitted with an <a href="http://dev.w3.org/html5/spec/Overview.html#html-mime-type">HTML MIME
  type</a>, such as <code><a href="http://dev.w3.org/html5/spec/Overview.html#text-html">text/html</a></code>, then it will be
  processed as an HTML document by Web browsers.

  
  This specification defines version 5 of the HTML syntax, known as
  "HTML5".

  </p><p>The second concrete syntax is the XHTML syntax, which is an
  application of XML. When a document is transmitted with an <a href="http://dev.w3.org/html5/spec/Overview.html#xml-mime-type">XML
  MIME type</a>, such as <code><a href="http://dev.w3.org/html5/spec/Overview.html#application-xhtml-xml">application/xhtml+xml</a></code>, then
  it is treated as an XML document by Web browsers, to be parsed by an
  XML processor. Authors are reminded that the processing for XML and
  HTML differs; in particular, even minor syntax errors will prevent a
  document labeled as XML from being rendered fully, whereas they
  would be ignored in the HTML syntax.

  
  This specification defines version 5 of the XHTML syntax, known as
  "XHTML5".

  </p><p>The DOM, the HTML syntax, and XML cannot all represent the same
  content. For example, namespaces cannot be represented using the
  HTML syntax, but they are supported in the DOM and in XML.
  Similarly, documents that use the <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-noscript-element">noscript</a></code> feature can
  be represented using the HTML syntax, but cannot be represented with
  the DOM or in XML. Comments that contain the string "<code title="">--&gt;</code>" can only be represented in the DOM, not in
  the HTML and XML syntaxes.</p><h3 id="structure-of-this-specification"><span class="secno">1.7 </span>Structure of this specification</h3><p><i>This section is non-normative.</i></p><p>This specification is divided into the following major
  sections:</p><dl><dt><a href="http://dev.w3.org/html5/spec/Overview.html#infrastructure">Common infrastructure</a></dt>

   <dd>The conformance classes, algorithms, definitions, and the
   common underpinnings of the rest of the specification.</dd>


   <dt><a href="http://dev.w3.org/html5/spec/Overview.html#dom">Semantics, structure, and APIs of HTML documents</a></dt>

   <dd>Documents are built from elements. These elements form a tree
   using the DOM. This section defines the features of this DOM, as
   well as introducing the features common to all elements, and the
   concepts used in defining elements.</dd>


   <dt><a href="http://dev.w3.org/html5/spec/Overview.html#semantics">The elements of HTML</a></dt>

   <dd>Each element has a predefined meaning, which is explained in
   this section. Rules for authors on how to use the element<span class="impl">, along with user agent requirements for how to handle
   each element,</span> are also given.</dd>


   <dt><a href="http://dev.w3.org/html5/spec/Overview.html#browsers">Loading Web pages</a></dt>

   <dd>HTML documents do not exist in a vacuum — this section
   defines many of the features that affect environments that deal
   with multiple pages.</dd>

   <dt><a href="http://dev.w3.org/html5/spec/Overview.html#webappapis">Web application APIs</a></dt>

   <dd>This section introduces basic features for scripting of
   applications in HTML.</dd>

   <dt><a href="http://dev.w3.org/html5/spec/Overview.html#editing">User interaction</a></dt>

   <dd>HTML documents can provide a number of mechanisms for users to
   interact with and modify content, which are described in this
   section.</dd>





   <dt><a href="http://dev.w3.org/html5/spec/Overview.html#syntax">The HTML syntax</a></dt>
   <dt><a href="http://dev.w3.org/html5/spec/Overview.html#xhtml">The XHTML syntax</a></dt>

   <dd>All of these features would be for naught if they couldn't be
   represented in a serialized form and sent to other people, and so
   these sections define the syntaxes of HTML, along with rules for
   how to parse content using those syntaxes.</dd>


  </dl><p>There are also some appendices, defining <a href="http://dev.w3.org/html5/spec/Overview.html#rendering">rendering rules</a> for Web browsers and listing
  <a href="http://dev.w3.org/html5/spec/Overview.html#obsolete">obsolete features</a> and <a href="http://dev.w3.org/html5/spec/Overview.html#iana">IANA
  considerations</a>.</p><h4 id="how-to-read-this-specification"><span class="secno">1.7.1 </span>How to read this specification</h4><p>This specification should be read like all other specifications.
  First, it should be read cover-to-cover, multiple times. Then, it
  should be read backwards at least once. Then it should be read by
  picking random sections from the contents list and following all the
  cross-references.</p><h4 id="typographic-conventions"><span class="secno">1.7.2 </span>Typographic conventions</h4><p>This is a definition, requirement, or explanation.</p><p class="note">This is a note.</p><p class="example">This is an example.</p><p class="XXX">This is an open issue.</p><p class="warning">This is a warning.</p><pre class="idl extract">interface <dfn title="">Example</dfn> {
  // this is an IDL definition
};</pre><dl class="domintro"><dt><var title="">variable</var> = <var title="">object</var> . <code title="">method</code>( [ <var title="">optionalArgument</var> ] )</dt>

   <dd>

    <p>This is a note to authors describing the usage of an interface.</p>

   </dd>

  </dl><pre class="css">/* this is a CSS fragment */</pre><p>The defining instance of a term is marked up like <dfn id="x-this" title="x-this">this</dfn>. Uses of that term are marked up like
  <a href="http://dev.w3.org/html5/spec/Overview.html#x-this" title="x-this">this</a> or like <i title="x-this"><a href="http://dev.w3.org/html5/spec/Overview.html#x-this">this</a></i>.</p><p>The defining instance of an element, attribute, or API is marked
  up like <dfn id="x-that" title="x-that"><code>this</code></dfn>. References to
  that element, attribute, or API are marked up like <code title="x-that"><a href="http://dev.w3.org/html5/spec/Overview.html#x-that">this</a></code>.</p><p>Other code fragments are marked up <code title="">like
  this</code>.</p><p>Variables are marked up like <var title="">this</var>.</p><p class="impl">This is an implementation requirement.</p><h3 id="a-quick-introduction-to-html"><span class="secno">1.8 </span>A quick introduction to HTML</h3><p><i>This section is non-normative.</i></p><p>A basic HTML document looks like this:</p><pre id="intro-early-example">&lt;!DOCTYPE html&gt;
&lt;html&gt;
 &lt;head&gt;
  &lt;title&gt;Sample page&lt;/title&gt;
 &lt;/head&gt;
 &lt;body&gt;
  &lt;h1&gt;Sample page&lt;/h1&gt;
  &lt;p&gt;This is a &lt;a href="demo.html"&gt;simple&lt;/a&gt; sample.&lt;/p&gt;
  &lt;!-- this is a comment --&gt;
 &lt;/body&gt;
&lt;/html&gt;</pre><p>HTML documents consist of a tree of elements and text. Each
  element is denoted in the source by a <a href="http://dev.w3.org/html5/spec/Overview.html#syntax-start-tag" title="syntax-start-tag">start tag</a>, such as "<code title="">&lt;body&gt;</code>", and an <a href="http://dev.w3.org/html5/spec/Overview.html#syntax-end-tag" title="syntax-end-tag">end
  tag</a>, such as "<code title="">&lt;/body&gt;</code>". (Certain
  start tags and end tags can in certain cases be <a href="http://dev.w3.org/html5/spec/Overview.html#syntax-tag-omission" title="syntax-tag-omission">omitted</a> and are implied by other
  tags.)</p><p>Tags have to be nested such that elements are all completely
  within each other, without overlapping:</p><pre class="bad">&lt;p&gt;This is &lt;em&gt;very &lt;strong&gt;wrong&lt;/em&gt;!&lt;/strong&gt;&lt;/p&gt;</pre><pre>&lt;p&gt;This &lt;em&gt;is &lt;strong&gt;correct&lt;/strong&gt;.&lt;/em&gt;&lt;/p&gt;</pre><p>This specification defines a set of elements that can be used in
  HTML, along with rules about the ways in which the elements can be
  nested.</p><p>Elements can have attributes, which control how the elements
  work. In the example below, there is a <a href="http://dev.w3.org/html5/spec/Overview.html#hyperlink">hyperlink</a>,
  formed using the <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-a-element">a</a></code> element and its <code title="attr-hyperlink-href"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-hyperlink-href">href</a></code> attribute:</p><pre>&lt;a href="demo.html"&gt;simple&lt;/a&gt;</pre><p><a href="http://dev.w3.org/html5/spec/Overview.html#syntax-attributes" title="syntax-attributes">Attributes</a> are placed
  inside the start tag, and consist of a <a href="http://dev.w3.org/html5/spec/Overview.html#syntax-attribute-name" title="syntax-attribute-name">name</a> and a <a href="http://dev.w3.org/html5/spec/Overview.html#syntax-attribute-value" title="syntax-attribute-value">value</a>, separated by an "<code title="">=</code>" character. The attribute value can remain <a href="http://dev.w3.org/html5/spec/Overview.html#unquoted">unquoted</a> if it doesn't contain spaces or any of
  <code title="">"</code> <code title="">'</code> <code title="">`</code> <code title="">=</code> <code title="">&lt;</code>
  or <code title="">&gt;</code>. Otherwise, it has to be quoted using
  either single or double quotes. The value, along with the "<code title="">=</code>" character, can be omitted altogether if the value
  is the empty string.</p><pre>&lt;!-- empty attributes --&gt;
&lt;input name=address disabled&gt;
&lt;input name=address disabled=""&gt;

&lt;!-- attributes with a value --&gt;
&lt;input name=address maxlength=200&gt;
&lt;input name=address maxlength='200'&gt;
&lt;input name=address maxlength="200"&gt;</pre><p>HTML user agents (e.g. Web browsers) then <i>parse</i> this
  markup, turning it into a DOM (Document Object Model) tree. A DOM
  tree is an in-memory representation of a document.</p><p>DOM trees contain several kinds of nodes, in particular a DOCTYPE
  node, elements, text nodes, and comment nodes.</p><p>The <a href="http://dev.w3.org/html5/spec/Overview.html#intro-early-example">markup snippet at the top of
  this section</a> would be turned into the following DOM tree:</p><ul class="domTree"><li class="t10">DOCTYPE: <code title="">html</code></li><li class="t1"><code><a href="http://dev.w3.org/html5/spec/Overview.html#the-html-element-0">html</a></code><ul><li class="t1"><code><a href="http://dev.w3.org/html5/spec/Overview.html#the-head-element-0">head</a></code><ul><li class="t3"><code>#text</code>: <span title="">⏎␣␣</span></li><li class="t1"><code><a href="http://dev.w3.org/html5/spec/Overview.html#the-title-element-0">title</a></code><ul><li class="t3"><code>#text</code>: <span title="">Sample page</span></li></ul></li><li class="t3"><code>#text</code>: <span title="">⏎␣</span></li></ul></li><li class="t3"><code>#text</code>: <span title="">⏎␣</span></li><li class="t1"><code><a href="http://dev.w3.org/html5/spec/Overview.html#the-body-element-0">body</a></code><ul><li class="t3"><code>#text</code>: <span title="">⏎␣␣</span></li><li class="t1"><code><a href="http://dev.w3.org/html5/spec/Overview.html#the-h1-h2-h3-h4-h5-and-h6-elements">h1</a></code><ul><li class="t3"><code>#text</code>: <span title="">Sample page</span></li></ul></li><li class="t3"><code>#text</code>: <span title="">⏎␣␣</span></li><li class="t1"><code><a href="http://dev.w3.org/html5/spec/Overview.html#the-p-element">p</a></code><ul><li class="t3"><code>#text</code>: <span title="">This is a </span></li><li class="t1"><code><a href="http://dev.w3.org/html5/spec/Overview.html#the-a-element">a</a></code> <span class="t2" title=""><code class="attribute name">href</code>="<code class="attribute value">demo.html</code>"</span><ul><li class="t3"><code>#text</code>: <span title="">simple</span></li></ul></li><li class="t3"><code>#text</code>: <span title=""> sample.</span></li></ul></li><li class="t3"><code>#text</code>: <span title="">⏎␣␣</span></li><li class="t8"><code>#comment</code>: <span title=""> this is a comment </span></li><li class="t3"><code>#text</code>: <span title="">⏎␣⏎</span></li></ul></li></ul></li></ul><p>The <a href="http://dev.w3.org/html5/spec/Overview.html#root-element">root element</a> of this tree is the
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-html-element-0">html</a></code> element, which is the element always found at the
  root of HTML documents. It contains two elements, <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-head-element-0">head</a></code>
  and <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-body-element-0">body</a></code>, as well as a text node between them.</p><p>There are many more text nodes in the DOM tree than one would
  initially expect, because the source contains a number of spaces
  (represented here by "␣") and line breaks ("⏎") that
  all end up as text nodes in the DOM. However, for historical reasons
  not all of the spaces and line breaks in the original markup appear
  in the DOM. In particular, all the whitespace before
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-head-element-0">head</a></code> start tag ends up being dropped silently, and all
  the whitespace after the <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-body-element-0">body</a></code> end tag ends up placed at
  the end of the <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-body-element-0">body</a></code>.</p><p>The <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-head-element-0">head</a></code> element contains a <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-title-element-0">title</a></code>
  element, which itself contains a text node with the text "Sample
  page". Similarly, the <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-body-element-0">body</a></code> element contains an
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-h1-h2-h3-h4-h5-and-h6-elements">h1</a></code> element, a <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-p-element">p</a></code> element, and a
  comment.</p><hr><p>This DOM tree can be manipulated from scripts in the
  page. Scripts (typically in JavaScript) are small programs that can
  be embedded using the <code><a href="http://dev.w3.org/html5/spec/Overview.html#script">script</a></code> element or using
  <a href="http://dev.w3.org/html5/spec/Overview.html#event-handler-content-attributes">event handler content attributes</a>. For example, here is
  a form with a script that sets the value of the form's
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-output-element">output</a></code> element to say "Hello World":</p><pre>&lt;<a href="http://dev.w3.org/html5/spec/Overview.html#the-form-element">form</a> <a href="http://dev.w3.org/html5/spec/Overview.html#attr-form-name" title="attr-form-name">name</a>="main"&gt;
 Result: &lt;<a href="http://dev.w3.org/html5/spec/Overview.html#the-output-element">output</a> <a href="http://dev.w3.org/html5/spec/Overview.html#attr-fe-name" title="attr-fe-name">name</a>="result"&gt;&lt;/output&gt;
 &lt;<a href="http://dev.w3.org/html5/spec/Overview.html#script">script</a>&gt;
  <a href="http://dev.w3.org/html5/spec/Overview.html#htmldocument" title="HTMLDocument">document</a>.<a href="http://dev.w3.org/html5/spec/Overview.html#dom-document-forms" title="dom-document-forms">forms</a>.main.<a href="http://dev.w3.org/html5/spec/Overview.html#dom-form-elements" title="dom-form-elements">elements</a>.result.<a href="http://dev.w3.org/html5/spec/Overview.html#dom-output-value" title="dom-output-value">value</a> = 'Hello World';
 &lt;/script&gt;
&lt;/form&gt;</pre><p>Each element in the DOM tree is represented by an object, and
  these objects have APIs so that they can be manipulated. For
  instance, a link (e.g. the <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-a-element">a</a></code> element in the tree above)
  can have its "<code title="attr-hyperlink-href"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-hyperlink-href">href</a></code>"
  attribute changed in several ways:</p><pre>var a = <a href="http://dev.w3.org/html5/spec/Overview.html#htmldocument" title="HTMLDocument">document</a>.<a href="http://dev.w3.org/html5/spec/Overview.html#dom-document-links" title="dom-document-links">links</a>[0]; // obtain the first link in the document
a.<a href="http://dev.w3.org/html5/spec/Overview.html#dom-a-href" title="dom-a-href">href</a> = 'sample.html'; // change the destination URL of the link
a.<a href="http://dev.w3.org/html5/spec/Overview.html#dom-uda-protocol" title="dom-uda-protocol">protocol</a> = 'https'; // change just the scheme part of the URL
a.setAttribute('href', 'http://example.com/'); // change the content attribute directly</pre><p>Since DOM trees are used as the way to represent HTML documents
  when they are processed and presented by implementations (especially
  interactive implementations like Web browsers), this specification
  is mostly phrased in terms of DOM trees, instead of the markup
  described above.</p><hr><p>HTML documents represent a media-independent description of
  interactive content. HTML documents might be rendered to a screen,
  or through a speech synthesizer, or on a braille display. To
  influence exactly how such rendering takes place, authors can use a
  styling language such as CSS.</p><p>In the following example, the page has been made yellow-on-blue
  using CSS.</p><pre>&lt;!DOCTYPE html&gt;
&lt;html&gt;
 &lt;head&gt;
  &lt;title&gt;Sample styled page&lt;/title&gt;
  &lt;style&gt;
   body { background: navy; color: yellow; }
  &lt;/style&gt;
 &lt;/head&gt;
 &lt;body&gt;
  &lt;h1&gt;Sample styled page&lt;/h1&gt;
  &lt;p&gt;This page is just a demo.&lt;/p&gt;
 &lt;/body&gt;
&lt;/html&gt;</pre><p>For more details on how to use HTML, authors are encouraged to
  consult tutorials and guides. Some of the examples included in this
  specification might also be of use, but the novice author is
  cautioned that this specification, by necessity, defines the
  language with a level of detail that might be difficult to
  understand at first.</p><h3 id="conformance-requirements-for-authors"><span class="secno">1.9 </span>Conformance requirements for authors</h3><p><i>This section is non-normative.</i></p><p>Unlike previous versions of the HTML specification, this
  specification defines in some detail the required processing for
  invalid documents as well as valid documents.</p><!-- This has led
  to some questioning the purpose of conformance criteria: if there is
  no ambiguity in how something will be processed, why disallow it? --><p>However, even though the processing of invalid content is in most
  cases well-defined, conformance requirements for documents are still
  important: in practice, interoperability (the situation in which all
  implementations process particular content in a reliable and
  identical or equivalent way) is not the only goal of document
  conformance requirements. This section details some of the more
  common reasons for still distinguishing between a conforming
  document and one with errors.</p><h4 id="presentational-markup"><span class="secno">1.9.1 </span>Presentational markup</h4><p><i>This section is non-normative.</i></p><p>The majority of presentational features from previous versions of
  HTML are no longer allowed. Presentational markup in general has
  been found to have a number of problems:</p><dl><dt>The use of presentational elements leads to poorer accessibility</dt>

   <dd>

    <p>While it is possible to use presentational markup in a way that
    provides users of assistive technologies (ATs) with an acceptable
    experience (e.g. using ARIA), doing so is significantly more
    difficult than doing so when using semantically-appropriate
    markup. Furthermore, even using such techniques doesn't help make
    pages accessible for non-AT non-graphical users, such as users of
    text-mode browsers.</p>

    <p>Using media-independent markup, on the other hand, provides an
    easy way for documents to be authored in such a way that they work
    for more users (e.g. text browsers).</p>

   </dd>


   <dt>Higher cost of maintenance</dt>

   <dd>

    <p>It is significantly easier to maintain a site written in such a
    way that the markup is style-independent. For example, changing
    the color of a site that uses <code>&lt;font&nbsp;color=""&gt;</code>
    throughout requires changes across the entire site, whereas a
    similar change to a site based on CSS can be done by changing a
    single file.</p>

   </dd>


   <dt>Higher document sizes</dt>

   <dd>

    <p>Presentational markup tends to be much more redundant, and thus
    results in larger document sizes.</p>

   </dd>

  </dl><p>For those reasons, presentational markup has been removed from
  HTML in this version. This change should not come as a surprise;
  HTML4 deprecated presentational markup many years ago and provided a
  mode (HTML4 Transitional) to help authors move away from
  presentational markup; later, XHTML 1.1 went further and obsoleted
  those features altogether.</p><p>The only remaining presentational markup features in HTML are the
  <code title="attr-style"><a href="http://dev.w3.org/html5/spec/Overview.html#the-style-attribute">style</a></code> attribute and the
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-style-element">style</a></code> element. Use of the <code title="attr-style"><a href="http://dev.w3.org/html5/spec/Overview.html#the-style-attribute">style</a></code> attribute is somewhat discouraged in
  production environments, but it can be useful for rapid prototyping
  (where its rules can be directly moved into a separate style sheet
  later) and for providing specific styles in unusual cases where a
  separate style sheet would be inconvenient. Similarly, the
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-style-element">style</a></code> element can be useful in syndication or for
  page-specific styles, but in general an external style sheet is
  likely to be more convenient when the styles apply to multiple
  pages.</p><p>It is also worth noting that some elements that were previously
  presentational have been redefined in this specification to be
  media-independent: <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-b-element">b</a></code>, <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-i-element">i</a></code>, <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-hr-element">hr</a></code>,
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-s-element">s</a></code>, and <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-small-element">small</a></code>.</p><h4 id="syntax-errors"><span class="secno">1.9.2 </span>Syntax errors</h4><p><i>This section is non-normative.</i></p><p>The syntax of HTML is constrained to avoid a wide variety of
  problems.</p><dl><dt>Unintuitive error-handling behavior</dt>

   <dd>

    <p>Certain invalid syntax constructs, when parsed, result in DOM
    trees that are highly unintuitive.</p>

    <div class="example">

     <p>For example, the following markup fragment results in a DOM
     with an <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-hr-element">hr</a></code> element that is an <em>earlier</em>
     sibling of the corresponding <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-table-element">table</a></code> element:</p>

     <pre class="bad">&lt;table&gt;&lt;hr&gt;...</pre>

    </div>

   </dd>


   <dt>Errors with optional error recovery</dt>

   <dd>

    <p>To allow user agents to be used in controlled environments
    without having to implement the more bizarre and convoluted error
    handling rules, user agents are permitted to fail whenever
    encountering a <a href="http://dev.w3.org/html5/spec/Overview.html#parse-error">parse error</a>.</p>

   </dd>


   <dt>Errors where the error-handling behavior is not compatible with streaming user agents</dt>

   <dd>

    <p>Some error-handling behavior, such as the behavior for the
    <code title="">&lt;table&gt;&lt;hr&gt;...</code> example mentioned
    above, are incompatible with streaming user agents. To avoid
    interoperability problems with such user agents, any syntax
    resulting in such behavior is considered invalid.</p>

   </dd>


   <dt>Errors that can result in infoset coercion</dt>

   <dd>

    <p>When a user agent based on XML is connected to an HTML parser,
    it is possible that certain invariants that XML enforces, such as
    comments never containing two consecutive hyphens, will be
    violated by an HTML file. Handling this can require that the
    parser coerce the HTML DOM into an XML-compatible infoset. Most
    syntax constructs that require such handling are considered
    invalid.</p>

   </dd>


   <dt>Errors that result in disproportionally poor performance</dt>

   <dd>

    <p>Certain syntax constructs can result in disproportionally poor
    performance. To discourage the use of such constructs, they are
    typically made non-conforming.</p>

    <div class="example">

     <p>For example, the following markup results in poor performance
     when hitting the highlighted end tag, since all the open elements
     are examined first to see if they match the close tag:</p>

     <pre class="bad">&lt;p&gt;&lt;em&gt;&lt;span&gt;&lt;span&gt;&lt;span&gt;...&lt;span&gt;&lt;span&gt;&lt;span&gt;<strong>&lt;/em&gt;</strong></pre>

    </div>

   </dd>


   <dt>Errors involving fragile syntax constructs</dt>

   <dd>

    <p>There are syntax constructs that, for historical reasons, are
    relatively fragile. To help reduce the number of users who
    accidentally run into such problems, they are made
    non-conforming.</p>

    <div class="example">

     <p>For example, the parsing of certain named character references
     in attributes happens even with the closing semicolon being
     omitted. It is safe to include an ampersand followed by letters
     that do not form a named character reference, but if the letters
     are changed to a string that <em>does</em> form a named character
     reference, they will be interpreted as that character instead.</p>

     <p>In this fragment, the attribute's value is "<code title="">?bill&amp;ted</code>":</p>

     <pre class="bad">&lt;a href="?bill&amp;ted"&gt;Bill and Ted&lt;/a&gt;</pre>

     <p>In the following fragment, however, the attribute's value is
     actually "<code title="">?art©</code>",
     <em>not</em> the intended "<code title="">?art&amp;copy</code>":</p>

     <pre class="bad">&lt;a href="?art&amp;copy"&gt;Art and Copy&lt;/a&gt;</pre>

     <p>To avoid this problem, all named character references are
     required to end with a semicolon, and uses of named character
     references without a semicolon are flagged as errors.</p>

     <p>Thus, the correct way to express the above cases is as
     follows:</p>

     <pre>&lt;a href="?bill&amp;ted"&gt;Bill and Ted&lt;/a&gt; &lt;!-- &amp;ted is ok, since it's not a named character reference --&gt;</pre>
     <pre>&lt;a href="?art&amp;amp;copy"&gt;Art and Copy&lt;/a&gt; &lt;!-- the &amp; has to be escaped, since &amp;copy <em>is</em> a named character reference --&gt;</pre>

    </div>

   </dd>


   <dt>Errors involving known interoperability problems in legacy user agents</dt>

   <dd>

    <p>Certain syntax constructs are known to cause especially subtle
    or serious problems in legacy user agents, and are therefore
    marked as non-conforming to help authors avoid them.</p>

    <div class="example">

     <p>For example, this is why the U+0060 GRAVE ACCENT character (`)
     is not allowed in unquoted attributes. In certain legacy user
     agents, <!-- namely IE --> it is sometimes treated as a quote
     character.</p>

    </div>

    <div class="example">

     <p>Another example of this is the DOCTYPE, which is required to
     trigger <a href="http://dev.w3.org/html5/spec/Overview.html#no-quirks-mode">no-quirks mode</a>, because the behavior of
     legacy user agents in <a href="http://dev.w3.org/html5/spec/Overview.html#quirks-mode">quirks mode</a> is often largely
     undocumented.</p>

    </div>

   </dd>


   <dt>Errors that risk exposing authors to security attacks</dt>

   <dd>

    <p>Certain restrictions exist purely to avoid known security
    problems.</p>

    <div class="example">

     <p>For example, the restriction on using UTF-7 exists purely to
     avoid authors falling prey to a known cross-site-scripting attack
     using UTF-7.</p>

    </div>

   </dd>


   <dt>Cases where the author's intent is unclear</dt>

   <dd>

    <p>Markup where the author's intent is very unclear is often made
    non-conforming. Correcting these errors early makes later
    maintenance easier.</p>

    <div class="example">

     <p>For example, it is unclear whether the author intended the
     following to be an <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-h1-h2-h3-h4-h5-and-h6-elements">h1</a></code> heading or an <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-h1-h2-h3-h4-h5-and-h6-elements">h2</a></code>
     heading:</p>

     <pre class="bad">&lt;h1&gt;Contact details&lt;/h2&gt;</pre>

    </div>

   </dd>


   <dt>Cases that are likely to be typos</dt>

   <dd>

    <p>When a user makes a simple typo, it is helpful if the error can
    be caught early, as this can save the author a lot of debugging
    time. This specification therefore usually considers it an error
    to use element names, attribute names, and so forth, that do not
    match the names defined in this specification.</p>

    <div class="example">

     <p>For example, if the author typed <code>&lt;capton&gt;</code>
     instead of <code>&lt;caption&gt;</code>, this would be flagged as an
     error and the author could correct the typo immediately.</p>

    </div>

   </dd>


   <dt>Errors that could interfere with new syntax in the future</dt>

   <dd>

    <p>In order to allow the language syntax to be extended in the
    future, certain otherwise harmless features are disallowed.</p>

    <div class="example">

     <p>For example, "attributes" in end tags are ignored currently,
     but they are invalid, in case a future change to the language
     makes use of that syntax feature without conflicting with
     already-deployed (and valid!) content.</p>

    </div>

   </dd>


  </dl><p>Some authors find it helpful to be in the practice of always
  quoting all attributes and always including all optional tags,
  preferring the consistency derived from such custom over the minor
  benefits of terseness afforded by making use of the flexibility of
  the HTML syntax. To aid such authors, conformance checkers can
  provide modes of operation wherein such conventions are
  enforced.</p><h4 id="restrictions-on-content-models-and-on-attribute-values"><span class="secno">1.9.3 </span>Restrictions on content models and on attribute values</h4><p><i>This section is non-normative.</i></p><p>Beyond the syntax of the language, this specification also places
  restrictions on how elements and attributes can be specified. These
  restrictions are present for similar reasons:</p><dl><dt>Errors involving content with dubious semantics</dt>

   <dd>

    <p>To avoid misuse of elements with defined meanings, content
    models are defined that restrict how elements can be nested when
    such nestings would be of dubious value.</p>

    <p class="example">For example, this specification disallows
    nesting a <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-section-element">section</a></code> element inside a <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-kbd-element">kbd</a></code>
    element, since it is highly unlikely for an author to indicate
    that an entire section should be keyed in.</p>

   </dd>


   <dt>Errors that involve a conflict in expressed semantics</dt>

   <dd>

    <p>Similarly, to draw the author's attention to mistakes in the
    use of elements, clear contradictions in the semantics expressed
    are also considered conformance errors.</p>

    <div class="example">

     <p>In the fragments below, for example, the semantics are
     nonsensical: a row cannot simultaneously be a cell, nor can a
     radio button be a progress bar.</p>

     <pre class="bad">&lt;tr role="cell"&gt;</pre>
     <pre class="bad">&lt;input type=radio role=progressbar&gt;</pre>

    </div>

    <p class="example">Another example is the restrictions on the
    content models of the <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-ul-element">ul</a></code> element, which only allows
    <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-li-element">li</a></code> element children. Lists by definition consist just
    of zero or more list items, so if a <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-ul-element">ul</a></code> element
    contains something other than an <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-li-element">li</a></code> element, it's not
    clear what was meant.</p>

   </dd>


   <dt>Cases where the default styles are likely to lead to confusion</dt>

   <dd>

    <p>Certain elements have default styles or behaviors that make
    certain combinations likely to lead to confusion. Where these have
    equivalent alternatives without this problem, the confusing
    combinations are disallowed.</p>

    <p class="example">For example, <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-div-element">div</a></code> elements are
    rendered as block boxes, and <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-span-element">span</a></code> elements as inline
    boxes. Putting a block box in an inline box is unnecessarily
    confusing; since either nesting just <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-div-element">div</a></code> elements, or
    nesting just <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-span-element">span</a></code> elements, or nesting
    <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-span-element">span</a></code> elements inside <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-div-element">div</a></code> elements all
    serve the same purpose as nesting a <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-div-element">div</a></code> element in a
    <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-span-element">span</a></code> element, but only the latter involves a block
    box in an inline box, the latter combination is disallowed.</p>

    <p class="example">Another example would be the way
    <a href="http://dev.w3.org/html5/spec/Overview.html#interactive-content">interactive content</a> cannot be nested. For example, a
    <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-button-element">button</a></code> element cannot contain a <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-textarea-element">textarea</a></code>
    element. This is because the default behavior of such nesting
    interactive elements would be highly confusing to users. Instead
    of nesting these elements, they can be placed side by side.</p>

   </dd>


   <dt>Errors that indicate a likely misunderstanding of the specification</dt>

   <dd>

    <p>Sometimes, something is disallowed because allowing it would
    likely cause author confusion.</p>

    <p class="example">For example, setting the <code title="attr-fe-disabled"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-fe-disabled">disabled</a></code> attribute to the value
    "<code title="">false</code>" is disallowed, because despite the
    appearance of meaning that the element is enabled, it in fact
    means that the element is <em>disabled</em> (what matters for
    implementations is the presence of the attribute, not its
    value).</p>

   </dd>


   <dt>Errors involving limits that have been imposed merely to simplify the language</dt>

   <dd>

    <p>Some conformance errors simplify the language that authors need
    to learn.</p>

    <p class="example">For example, the <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-area-element">area</a></code> element's
    <code title="attr-area-shape"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-area-shape">shape</a></code> attribute, despite
    accepting both <code title="attr-area-shape-keyword-circ"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-area-shape-keyword-circ">circ</a></code> and <code title="attr-area-shape-keyword-circle"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-area-shape-keyword-circle">circle</a></code> values in
    practice as synonyms, disallows the use of the <code title="attr-area-shape-keyword-circ"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-area-shape-keyword-circ">circ</a></code> value, so as to
    simplify tutorials and other learning aids. There would be no
    benefit to allowing both, but it would cause extra confusion when
    teaching the language.</p>

   </dd>


   <dt>Errors that involve peculiarities of the parser</dt>

   <dd>

    <p>Certain elements are parsed in somewhat eccentric ways
    (typically for historical reasons), and their content model
    restrictions are intended to avoid exposing the author to these
    issues.</p>

    <div class="example">

     <p>For example, a <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-form-element">form</a></code> element isn't allowed inside
     <a href="http://dev.w3.org/html5/spec/Overview.html#phrasing-content">phrasing content</a>, because when parsed as HTML, a
     <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-form-element">form</a></code> element's start tag will imply a <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-p-element">p</a></code>
     element's end tag. Thus, the following markup results in two
     <a href="http://dev.w3.org/html5/spec/Overview.html#paragraph" title="paragraph">paragraphs</a>, not one:</p>

     <pre>&lt;p&gt;Welcome. &lt;form&gt;&lt;label&gt;Name:&lt;/label&gt; &lt;input&gt;&lt;/form&gt;</pre>

     <p>It is parsed exactly like the following:</p>

     <pre>&lt;p&gt;Welcome. &lt;/p&gt;&lt;form&gt;&lt;label&gt;Name:&lt;/label&gt; &lt;input&gt;&lt;/form&gt;</pre>

    </div>

   </dd>


   <dt>Errors that would likely result in scripts failing in hard-to-debug ways</dt>

   <dd>

    <p>Some errors are intended to help prevent script problems that
    would be hard to debug.</p>

    <p class="example">This is why, for instance, it is non-conforming
    to have two <code title="attr-id"><a href="http://dev.w3.org/html5/spec/Overview.html#the-id-attribute">id</a></code> attributes with the
    same value. Duplicate IDs lead to the wrong element being
    selected, with sometimes disastrous effects whose cause is hard to
    determine.</p>

   </dd>


   <dt>Errors that waste authoring time</dt>

   <dd>

    <p>Some constructs are disallowed because historically they have
    been the cause of a lot of wasted authoring time, and by
    encouraging authors to avoid making them, authors can save time in
    future efforts.</p>

    <p class="example">For example, a <code><a href="http://dev.w3.org/html5/spec/Overview.html#script">script</a></code> element's
    <code title="attr-script-src"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-script-src">src</a></code> attribute causes the
    element's contents to be ignored. However, this isn't obvious,
    especially if the element's contents appear to be executable
    script — which can lead to authors spending a lot of time
    trying to debug the inline script without realizing that it is not
    executing. To reduce this problem, this specification makes it
    non-conforming to have executable script in a <code><a href="http://dev.w3.org/html5/spec/Overview.html#script">script</a></code>
    element when the <code title="attr-script-src"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-script-src">src</a></code>
    attribute is present. This means that authors who are validating
    their documents are less likely to waste time with this kind of
    mistake.</p>

   </dd>


   <dt>Errors that involve areas that affect authors migrating to and from XHTML</dt>

   <dd>

    <p>Some authors like to write files that can be interpreted as
    both XML and HTML with similar results. Though this practice is
    discouraged in general due to the myriad of subtle complications
    involved (especially when involving scripting, styling, or any
    kind of automated serialization), this specification has a few
    restrictions intended to at least somewhat mitigate the
    difficulties. This makes it easier for authors to use this as a
    transitionary step when migrating between HTML and XHTML.</p>

    <p class="example">For example, there are somewhat complicated
    rules surrounding the <code title="attr-lang"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-lang">lang</a></code> and
    <code title="attr-xml-lang"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-xml-lang">xml:lang</a></code> attributes intended
    to keep the two synchronized.</p>

    <p class="example">Another example would be the restrictions on
    the values of <code title="">xmlns</code> attributes in the HTML
    serialization, which are intended to ensure that elements in
    conforming documents end up in the same namespaces whether
    processed as HTML or XML.</p>

   </dd>


   <dt>Errors that involve areas reserved for future expansion</dt>

   <dd>

    <p>As with the restrictions on the syntax intended to allow for
    new syntax in future revisions of the language, some restrictions
    on the content models of elements and values of attributes are
    intended to allow for future expansion of the HTML vocabulary.</p>

    <p class="example">For example, limiting the values of the <code title="attr-hyperlink-target"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-hyperlink-target">target</a></code> attribute that start
    with an U+005F LOW LINE character (_) to only specific predefined
    values allows new predefined values to be introduced at a future
    time without conflicting with author-defined values.</p>

   </dd>


   <dt>Errors that indicate a mis-use of other specifications</dt>

   <dd>

    <p>Certain restrictions are intended to support the restrictions
    made by other specifications.</p>

    <p class="example">For example, requiring that attributes that
    take media queries use only <em>valid</em> media queries
    reinforces the importance of following the conformance rules of
    that specification.</p>

   </dd>

  </dl><h3 id="recommended-reading"><span class="secno">1.10 </span>Recommended reading</h3><p><i>This section is non-normative.</i></p><p>The following documents might be of interest to readers of this
  specification.</p><dl><dt><cite>Character Model for the World Wide Web 1.0: Fundamentals</cite> <a href="http://dev.w3.org/html5/spec/Overview.html#refsCHARMOD">[CHARMOD]</a></dt>

   <dd><blockquote><p>This Architectural Specification provides
   authors of specifications, software developers, and content
   developers with a common reference for interoperable text
   manipulation on the World Wide Web, building on the Universal
   Character Set, defined jointly by the Unicode Standard and ISO/IEC
   10646. Topics addressed include use of the terms 'character',
   'encoding' and 'string', a reference processing model, choice and
   identification of character encodings, character escaping, and
   string indexing.</p></blockquote></dd>

   <dt><cite>Unicode Security Considerations</cite> <a href="http://dev.w3.org/html5/spec/Overview.html#refsUTR36">[UTR36]</a></dt>

   <dd><blockquote><p>Because Unicode contains such a large number of
   characters and incorporates the varied writing systems of the
   world, incorrect usage can expose programs or systems to possible
   security attacks. This is especially important as more and more
   products are internationalized. This document describes some of the
   security considerations that programmers, system analysts,
   standards developers, and users should take into account, and
   provides specific recommendations to reduce the risk of
   problems.</p></blockquote></dd>

   <dt><cite>Web Content Accessibility Guidelines (WCAG) 2.0</cite> <a href="http://dev.w3.org/html5/spec/Overview.html#refsWCAG">[WCAG]</a></dt>

   <dd><blockquote><p>Web Content Accessibility Guidelines (WCAG) 2.0
   covers a wide range of recommendations for making Web content more
   accessible. Following these guidelines will make content accessible
   to a wider range of people with disabilities, including blindness
   and low vision, deafness and hearing loss, learning disabilities,
   cognitive limitations, limited movement, speech disabilities,
   photosensitivity and combinations of these. Following these
   guidelines will also often make your Web content more usable to
   users in general.</p></blockquote></dd>

   <dt class="impl"><cite>Authoring Tool Accessibility Guidelines (ATAG) 2.0</cite> <a href="http://dev.w3.org/html5/spec/Overview.html#refsATAG">[ATAG]</a></dt>

   <dd class="impl"><blockquote><p>This specification provides
   guidelines for designing Web content authoring tools that are more
   accessible for people with disabilities. An authoring tool that
   conforms to these guidelines will promote accessibility by
   providing an accessible user interface to authors with disabilities
   as well as by enabling, supporting, and promoting the production of
   accessible Web content by all authors.</p></blockquote></dd>

   <dt class="impl"><cite>User Agent Accessibility Guidelines (UAAG) 2.0</cite> <a href="http://dev.w3.org/html5/spec/Overview.html#refsUAAG">[UAAG]</a></dt>

   <dd class="impl"><blockquote><p>This document provides guidelines
   for designing user agents that lower barriers to Web accessibility
   for people with disabilities. User agents include browsers and
   other types of software that retrieve and render Web content. A
   user agent that conforms to these guidelines will promote
   accessibility through its own user interface and through other
   internal facilities, including its ability to communicate with
   other technologies (especially assistive
   technologies). Furthermore, all users, not just users with
   disabilities, should find conforming user agents to be more
   usable.</p></blockquote></dd>

   <dt><cite>Polyglot Markup: HTML-Compatible XHTML Documents</cite> <a href="http://dev.w3.org/html5/spec/Overview.html#refsPOLYGLOT">[POLYGLOT]</a></dt>

   <dd><blockquote><p>A document that uses polyglot markup is document
   that is a stream of bytes that parses into identical document trees
   (with the exception of the xmlns attribute on the root element)
   when processed as HTML and when processed as XML. Polyglot markup
   that meets a well defined set of constraints is interpreted as
   compatible, regardless of whether they are processed as HTML or as
   XHTML, per the HTML5 specification. Polyglot markup uses a specific
   DOCTYPE, namespace declarations, and a specific case —
   normally lower case but occasionally camel case — for element
   and attribute names. Polyglot markup uses lower case for certain
   attribute values. Further constraints include those on empty
   elements, named entity references, and the use of scripts and
   style.</p></blockquote></dd>

  </dl><h2 id="infrastructure"><span class="secno">2 </span>Common infrastructure</h2><h3 id="terminology"><span class="secno">2.1 </span>Terminology</h3><p>This specification refers to both HTML and XML attributes and IDL
  attributes, often in the same context. When it is not clear which is
  being referred to, they are referred to as <dfn title="">content
  attributes</dfn> for HTML and XML attributes, and <dfn title="">IDL
  attributes</dfn> for those defined on IDL interfaces. Similarly, the
  term "properties" is used for both JavaScript object properties and
  CSS properties. When these are ambiguous they are qualified as <dfn title="">object properties</dfn> and <dfn title="">CSS
  properties</dfn> respectively.</p><p>Generally, when the specification states that a feature applies
  to <a href="http://dev.w3.org/html5/spec/Overview.html#syntax">the HTML syntax</a> or <a href="http://dev.w3.org/html5/spec/Overview.html#the-xhtml-syntax">the XHTML syntax</a>, it
  also includes the other. When a feature specifically only applies to
  one of the two languages, it is called out by explicitly stating
  that it does not apply to the other format, as in "for HTML,
  ... (this does not apply to XHTML)".</p><p>This specification uses the term <dfn title="">document</dfn> to
  refer to any use of HTML, ranging from short static documents to
  long essays or reports with rich multimedia, as well as to
  fully-fledged interactive applications.</p><p>For simplicity, terms such as <dfn title="">shown</dfn>, <dfn title="">displayed</dfn>, and <dfn title="">visible</dfn> might
  sometimes be used when referring to the way a document is rendered
  to the user. These terms are not meant to imply a visual medium;
  they must be considered to apply to other media in equivalent
  ways.</p><div class="impl">

  <p>When an algorithm B says to return to another algorithm A, it
  implies that A called B. Upon returning to A, the implementation
  must continue from where it left off in calling B.</p>

  </div><h4 id="resources"><span class="secno">2.1.1 </span>Resources</h4><p>The specification uses the term <dfn title="">supported</dfn>
  when referring to whether a user agent has an implementation capable
  of decoding the semantics of an external resource. A format or type
  is said to be <i>supported</i> if the implementation can process an
  external resource of that format or type without critical aspects of
  the resource being ignored. Whether a specific resource is
  <i>supported</i> can depend on what features of the resource's
  format are in use.</p><p class="example">For example, a PNG image would be considered to
  be in a supported format if its pixel data could be decoded and
  rendered, even if, unbeknownst to the implementation, the image also
  contained animation data.</p><p class="example">A MPEG4 video file would not be considered to be
  in a supported format if the compression format used was not
  supported, even if the implementation could determine the dimensions
  of the movie from the file's metadata.</p><p>What some specifications, in particular the HTTP and URI
  specifications, refer to as a <i>representation</i> is referred to
  in this specification as a <dfn title="">resource</dfn>. <a href="http://dev.w3.org/html5/spec/Overview.html#refsHTTP">[HTTP]</a> <a href="http://dev.w3.org/html5/spec/Overview.html#refsRFC3986">[RFC3986]</a></p><p>The term <dfn id="mime-type">MIME type</dfn> is used to refer to what is
  sometimes called an <i>Internet media type</i> in protocol
  literature. The term <i>media type</i> in this specification is used
  to refer to the type of media intended for presentation, as used by
  the CSS specifications. <a href="http://dev.w3.org/html5/spec/Overview.html#refsRFC2046">[RFC2046]</a> <a href="http://dev.w3.org/html5/spec/Overview.html#refsMQ">[MQ]</a></p><p>A string is a <dfn id="valid-mime-type">valid MIME type</dfn> if it matches the <code title="">media-type</code> rule defined in section 3.7 "Media Types"
  of RFC 2616. In particular, a <a href="http://dev.w3.org/html5/spec/Overview.html#valid-mime-type">valid MIME type</a> may
  include MIME type parameters. <a href="http://dev.w3.org/html5/spec/Overview.html#refsHTTP">[HTTP]</a></p><p>A string is a <dfn id="valid-mime-type-with-no-parameters">valid MIME type with no parameters</dfn> if it
  matches the <code title="">media-type</code> rule defined in section
  3.7 "Media Types" of RFC 2616, but does not contain any U+003B
  SEMICOLON characters (;). In other words, if it consists only of a
  type and subtype, with no MIME Type parameters. <a href="http://dev.w3.org/html5/spec/Overview.html#refsHTTP">[HTTP]</a></p><p>The term <dfn id="html-mime-type">HTML MIME type</dfn> is used to refer to the <a href="http://dev.w3.org/html5/spec/Overview.html#mime-type" title="MIME type">MIME types</a> <code><a href="http://dev.w3.org/html5/spec/Overview.html#text-html">text/html</a></code> and
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#text-html-sandboxed">text/html-sandboxed</a></code>.</p><p>A resource's <dfn id="critical-subresources">critical subresources</dfn> are those that the
  resource needs to have available to be correctly processed. Which
  resources are considered critical or not is defined by the
  specification that defines the resource's format. For CSS resources,
  only <code title="">@import</code> rules introduce <a href="http://dev.w3.org/html5/spec/Overview.html#critical-subresources">critical
  subresources</a>; other resources, e.g. fonts or backgrounds, are
  not.</p><h4 id="xml"><span class="secno">2.1.2 </span>XML</h4><p id="html-namespace">To ease migration from HTML to XHTML, UAs
  conforming to this specification will place elements in HTML in the
  <code>http://www.w3.org/1999/xhtml</code> namespace, at least for
  the purposes of the DOM and CSS. The term "<dfn id="html-elements">HTML
  elements</dfn>", when used in this specification, refers to any
  element in that namespace, and thus refers to both HTML and XHTML
  elements.</p><p>Except where otherwise stated, all elements defined or mentioned
  in this specification are in the
  <code>http://www.w3.org/1999/xhtml</code> namespace, and all
  attributes defined or mentioned in this specification have no
  namespace.</p><p>Attribute names are said to be <dfn id="xml-compatible">XML-compatible</dfn> if they
  match the <a href="http://www.w3.org/TR/REC-xml/#NT-Name"><code title="">Name</code></a> production defined in XML, they contain no
  U+003A COLON characters (:), and their first three characters are
  not an <a href="http://dev.w3.org/html5/spec/Overview.html#ascii-case-insensitive">ASCII case-insensitive</a> match for the string
  "<code title="">xml</code>". <a href="http://dev.w3.org/html5/spec/Overview.html#refsXML">[XML]</a></p><p>The term <dfn id="xml-mime-type">XML MIME type</dfn> is used to refer to the <a href="http://dev.w3.org/html5/spec/Overview.html#mime-type" title="MIME type">MIME types</a> <code title="">text/xml</code>,
  <code title="">application/xml</code>, and any <a href="http://dev.w3.org/html5/spec/Overview.html#mime-type">MIME
  type</a> whose subtype ends with the four characters "<code title="">+xml</code>". <a href="http://dev.w3.org/html5/spec/Overview.html#refsRFC3023">[RFC3023]</a></p><h4 id="dom-trees"><span class="secno">2.1.3 </span>DOM trees</h4><p>The term <dfn id="root-element">root element</dfn>, when not explicitly qualified
  as referring to the document's root element, means the furthest
  ancestor element node of whatever node is being discussed, or the
  node itself if it has no ancestors. When the node is a part of the
  document, then the node's <a href="http://dev.w3.org/html5/spec/Overview.html#root-element">root element</a> is indeed the
  document's root element; however, if the node is not currently part
  of the document tree, the root element will be an orphaned node.</p><p>When an element's <a href="http://dev.w3.org/html5/spec/Overview.html#root-element">root element</a> is the root element
  of a <code><a href="http://dev.w3.org/html5/spec/Overview.html#document">Document</a></code>, it is said to be <dfn id="in-a-document">in a
  <code>Document</code></dfn>. An element is said to have been <dfn id="insert-an-element-into-a-document" title="insert an element into a document">inserted into a
  document</dfn> when its <a href="http://dev.w3.org/html5/spec/Overview.html#root-element">root element</a> changes and is now
  the document's <a href="http://dev.w3.org/html5/spec/Overview.html#root-element">root element</a>. Analogously, an element is
  said to have been <dfn id="remove-an-element-from-a-document" title="remove an element from a
  document">removed from a document</dfn> when its <a href="http://dev.w3.org/html5/spec/Overview.html#root-element">root
  element</a> changes from being the document's <a href="http://dev.w3.org/html5/spec/Overview.html#root-element">root
  element</a> to being another element.</p><p>A node's <dfn id="home-subtree">home subtree</dfn> is the subtree rooted at that
  node's <a href="http://dev.w3.org/html5/spec/Overview.html#root-element">root element</a>. When a node is <a href="http://dev.w3.org/html5/spec/Overview.html#in-a-document">in a
  <code>Document</code></a>, its <a href="http://dev.w3.org/html5/spec/Overview.html#home-subtree">home subtree</a> is that
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#document">Document</a></code>'s tree.</p><p>The <code><a href="http://dev.w3.org/html5/spec/Overview.html#document">Document</a></code> of a <code><a href="http://dev.w3.org/html5/spec/Overview.html#node">Node</a></code> (such as an
  element) is the <code><a href="http://dev.w3.org/html5/spec/Overview.html#document">Document</a></code> that the <code><a href="http://dev.w3.org/html5/spec/Overview.html#node">Node</a></code>'s
  <code title="dom-Node-ownerDocument"><a href="http://dev.w3.org/html5/spec/Overview.html#dom-node-ownerdocument">ownerDocument</a></code> IDL
  attribute returns. When a <code><a href="http://dev.w3.org/html5/spec/Overview.html#node">Node</a></code> is <a href="http://dev.w3.org/html5/spec/Overview.html#in-a-document">in a
  <code>Document</code></a> then that <code><a href="http://dev.w3.org/html5/spec/Overview.html#document">Document</a></code> is
  always the <code><a href="http://dev.w3.org/html5/spec/Overview.html#node">Node</a></code>'s <code><a href="http://dev.w3.org/html5/spec/Overview.html#document">Document</a></code>, and the
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#node">Node</a></code>'s <code title="dom-Node-ownerDocument"><a href="http://dev.w3.org/html5/spec/Overview.html#dom-node-ownerdocument">ownerDocument</a></code> IDL attribute
  thus always returns that <code><a href="http://dev.w3.org/html5/spec/Overview.html#document">Document</a></code>.</p><p>The term <dfn id="tree-order">tree order</dfn> means a pre-order, depth-first
  traversal of DOM nodes involved (through the <code title="dom-Node-parentNode"><a href="http://dev.w3.org/html5/spec/Overview.html#dom-node-parentnode">parentNode</a></code>/<code title="dom-Node-childNodes"><a href="http://dev.w3.org/html5/spec/Overview.html#dom-node-childnodes">childNodes</a></code> relationship).</p><p>When it is stated that some element or attribute is <dfn id="ignore" title="ignore">ignored</dfn>, or treated as some other value, or
  handled as if it was something else, this refers only to the
  processing of the node after it is in the DOM. <span class="impl">A
  user agent must not mutate the DOM in such situations.</span></p><p>The term <dfn id="text-node">text node</dfn> refers to any <code><a href="http://dev.w3.org/html5/spec/Overview.html#text">Text</a></code>
  node, including <code><a href="http://dev.w3.org/html5/spec/Overview.html#cdatasection">CDATASection</a></code> nodes; specifically, any
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#node">Node</a></code> with node type <code title="">TEXT_NODE</code> (3)
  or <code title="">CDATA_SECTION_NODE</code> (4). <a href="http://dev.w3.org/html5/spec/Overview.html#refsDOMCORE">[DOMCORE]</a></p><p>A content attribute is said to <dfn title="">change</dfn> value
  only if its new value is different than its previous value; setting
  an attribute to a value it already has does not change it.</p><p>The term <dfn title="">empty</dfn>, when used of an attribute
  value, text node, or string, means that the length of the text is
  zero (i.e. not even containing spaces or control characters).</p><h4 id="scripting-0"><span class="secno">2.1.4 </span>Scripting</h4><p>The construction "a <code>Foo</code> object", where
  <code>Foo</code> is actually an interface, is sometimes used instead
  of the more accurate "an object implementing the interface
  <code>Foo</code>".</p><p>An IDL attribute is said to be <dfn title="">getting</dfn> when
  its value is being retrieved (e.g. by author script), and is said to
  be <dfn title="">setting</dfn> when a new value is assigned to
  it.</p><p>If a DOM object is said to be <dfn id="live">live</dfn>, then the
  attributes and methods on that object <span class="impl">must</span>
  operate on the actual underlying data, not a snapshot of the
  data.</p><p>The terms <dfn title="">fire</dfn> and <dfn title="">dispatch</dfn> are used interchangeably in the context of
  events, as in the DOM Events specifications. The term <dfn id="concept-events-trusted" title="concept-events-trusted">trusted event</dfn> is used as
  defined by the DOM Events specification. <!--
  http://krijnhoetmer.nl/irc-logs/webapps/20091218 --> <a href="http://dev.w3.org/html5/spec/Overview.html#refsDOMEVENTS">[DOMEVENTS]</a></p><h4 id="plugins"><span class="secno">2.1.5 </span>Plugins</h4><p>The term <dfn id="plugin">plugin</dfn> refers to a user-agent defined set of
  content handlers used by the user agent that can take part in the
  user agent's rendering of a <code><a href="http://dev.w3.org/html5/spec/Overview.html#document">Document</a></code> object, but that
  neither act as <a href="http://dev.w3.org/html5/spec/Overview.html#child-browsing-context" title="child browsing context">child browsing
  contexts</a> of the <code><a href="http://dev.w3.org/html5/spec/Overview.html#document">Document</a></code> nor introduce any
  <code><a href="http://dev.w3.org/html5/spec/Overview.html#node">Node</a></code> objects to the <code><a href="http://dev.w3.org/html5/spec/Overview.html#document">Document</a></code>'s DOM.</p><p>Typically such content handlers are provided by third parties,
  though a user agent can also designate built-in content handlers as
  plugins.</p><p>A user agent must not consider the types <code>text/plain</code>
  and <code>application/octet-stream</code> as having a registered
  <a href="http://dev.w3.org/html5/spec/Overview.html#plugin">plugin</a>.</p><!-- because of the way <object> handles
  those types, if nothing else (it also doesn't make any sense to have
  a plugin registered for those types, of course) --><p class="example">One example of a plugin would be a PDF viewer
  that is instantiated in a <a href="http://dev.w3.org/html5/spec/Overview.html#browsing-context">browsing context</a> when the
  user navigates to a PDF file. This would count as a plugin
  regardless of whether the party that implemented the PDF viewer
  component was the same as that which implemented the user agent
  itself. However, a PDF viewer application that launches separate
  from the user agent (as opposed to using the same interface) is not
  a plugin by this definition.</p><p class="note">This specification does not define a mechanism for
  interacting with plugins, as it is expected to be user-agent- and
  platform-specific. Some UAs might opt to support a plugin mechanism
  such as the Netscape Plugin API; others might use remote content
  converters or have built-in support for certain types. <a href="http://dev.w3.org/html5/spec/Overview.html#refsNPAPI">[NPAPI]</a></p><p class="warning">Browsers should take extreme care when
  interacting with external content intended for <a href="http://dev.w3.org/html5/spec/Overview.html#plugin" title="plugin">plugins</a>. When third-party software is run with
  the same privileges as the user agent itself, vulnerabilities in the
  third-party software become as dangerous as those in the user
  agent.</p><h4 id="character-encodings"><span class="secno">2.1.6 </span>Character encodings</h4><p class="XXX annotation"><span><a href="http://www.w3.org/html/wg/tracker/issues/101">ISSUE-101</a> (us-ascii-ref) blocks progress to Last Call</span></p><p>The <dfn id="preferred-mime-name">preferred MIME name</dfn> of a character encoding is the
  name or alias labeled as "preferred MIME name" in the IANA
  <cite>Character Sets</cite> registry, if there is one, or the
  encoding's name, if none of the aliases are so labeled. <a href="http://dev.w3.org/html5/spec/Overview.html#refsIANACHARSET">[IANACHARSET]</a></p><p>An <dfn id="ascii-compatible-character-encoding">ASCII-compatible character encoding</dfn> is a
  single-byte or variable-length encoding in which the bytes 0x09,
  0x0A, 0x0C, 0x0D, 0x20 - 0x22, 0x26, 0x27, 0x2C - 0x3F, 0x41 - 0x5A,
  and 0x61 - 0x7A<!-- is that list ok? do any character sets we want
  to support do things outside that range?  -->, ignoring bytes that
  are the second and later bytes of multibyte sequences, all
  correspond to single-byte sequences that map to the same Unicode
  characters as those bytes in ANSI_X3.4-1968 (US-ASCII). <a href="http://dev.w3.org/html5/spec/Overview.html#refsRFC1345">[RFC1345]</a></p><p class="note">This includes such encodings as Shift_JIS,
  HZ-GB-2312, and variants of ISO-2022, even though it is possible in
  these encodings for bytes like 0x70 to be part of longer sequences
  that are unrelated to their interpretation as ASCII. It excludes
  such encodings as UTF-7, UTF-16, GSM03.38, and EBCDIC variants.</p><!--
   We'll have to change that if anyone comes up with a way to have a
   document that is valid as two different encodings at once, with
   different <meta charset> elements applying in each case.
  --><p>The term <dfn title="">Unicode character</dfn> is used to mean a
  <i title="">Unicode scalar value</i> (i.e. any Unicode code point
  that is not a surrogate code point). <a href="http://dev.w3.org/html5/spec/Overview.html#refsUNICODE">[UNICODE]</a></p><h3 id="conformance-requirements"><span class="secno">2.2 </span>Conformance requirements</h3><p>All diagrams, examples, and notes in this specification are
  non-normative, as are all sections explicitly marked non-normative.
  Everything else in this specification is normative.</p><p>The key words "MUST", "MUST NOT", "REQUIRED", <!--"SHALL", "SHALL
  NOT",--> "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
  "OPTIONAL" in the normative parts of this document are to be
  interpreted as described in RFC2119. For readability, these words do
  not appear in all uppercase letters in this specification. <a href="http://dev.w3.org/html5/spec/Overview.html#refsRFC2119">[RFC2119]</a></p><p class="impl">Requirements phrased in the imperative as part of
  algorithms (such as "strip any leading space characters" or "return
  false and abort these steps") are to be interpreted with the meaning
  of the key word ("must", "should", "may", etc) used in introducing
  the algorithm.</p><p>This specification describes the conformance criteria for <span class="impl">user agents (relevant to implementors) and</span>
  documents<span class="impl"> (relevant to authors and authoring tool
  implementors)</span>.</p><p><dfn id="conforming-documents">Conforming documents</dfn> are those that comply with all
  the conformance criteria for documents. For readability, some of
  these conformance requirements are phrased as conformance
  requirements on authors; such requirements are implicitly
  requirements on documents: by definition, all documents are assumed
  to have had an author. (In some cases, that author may itself be a
  user agent — such user agents are subject to additional rules,
  as explained below.)</p><p class="example">For example, if a requirement states that
  "authors must not use the <code title="">foobar</code> element", it
  would imply that documents are not allowed to contain elements named
  <code title="">foobar</code>.</p><div class="impl">



  <p>User agents fall into several (overlapping) categories with
  different conformance requirements.</p>

  <dl><dt id="interactive">Web browsers and other interactive user agents</dt>

   <dd>

    <p>Web browsers that support <a href="http://dev.w3.org/html5/spec/Overview.html#the-xhtml-syntax">the XHTML syntax</a> must
    process elements and attributes from the <a href="http://dev.w3.org/html5/spec/Overview.html#html-namespace-0">HTML
    namespace</a> found in XML documents as described in this
    specification, so that users can interact with them, unless the
    semantics of those elements have been overridden by other
    specifications.</p>

    <p class="example">A conforming XHTML processor would, upon
    finding an XHTML <code><a href="http://dev.w3.org/html5/spec/Overview.html#script">script</a></code> element in an XML document,
    execute the script contained in that element. However, if the
    element is found within a transformation expressed in XSLT
    (assuming the user agent also supports XSLT), then the processor
    would instead treat the <code><a href="http://dev.w3.org/html5/spec/Overview.html#script">script</a></code> element as an opaque
    element that forms part of the transform.</p>

    <p>Web browsers that support <a href="http://dev.w3.org/html5/spec/Overview.html#syntax">the HTML syntax</a> must
    process documents labeled with an <a href="http://dev.w3.org/html5/spec/Overview.html#html-mime-type">HTML MIME type</a> as
    described in this specification, so that users can interact with
    them.</p>

    <p>User agents that support scripting must also be conforming
    implementations of the IDL fragments in this specification, as
    described in the Web IDL specification. <a href="http://dev.w3.org/html5/spec/Overview.html#refsWEBIDL">[WEBIDL]</a></p>

    <p class="note">Unless explicitly stated, specifications that
    override the semantics of HTML elements do not override the
    requirements on DOM objects representing those elements. For
    example, the <code><a href="http://dev.w3.org/html5/spec/Overview.html#script">script</a></code> element in the example above
    would still implement the <code><a href="http://dev.w3.org/html5/spec/Overview.html#htmlscriptelement">HTMLScriptElement</a></code>
    interface.</p>

   </dd>

   <dt id="non-interactive">Non-interactive presentation user agents</dt>

   <dd>

    <p>User agents that process HTML and XHTML documents purely to
    render non-interactive versions of them must comply to the same
    conformance criteria as Web browsers, except that they are exempt
    from requirements regarding user interaction.</p>

    <p class="note">Typical examples of non-interactive presentation
    user agents are printers (static UAs) and overhead displays
    (dynamic UAs). It is expected that most static non-interactive
    presentation user agents will also opt to <a href="http://dev.w3.org/html5/spec/Overview.html#non-scripted">lack scripting support</a>.</p>

    <p class="example">A non-interactive but dynamic presentation UA
    would still execute scripts, allowing forms to be dynamically
    submitted, and so forth. However, since the concept of "focus" is
    irrelevant when the user cannot interact with the document, the UA
    would not need to support any of the focus-related DOM APIs.</p>

   </dd>

   <dt><dfn id="non-scripted">User agents with no scripting support</dfn></dt>

   <dd>

    <p>Implementations that do not support scripting (or which have
    their scripting features disabled entirely) are exempt from
    supporting the events and DOM interfaces mentioned in this
    specification. For the parts of this specification that are
    defined in terms of an events model or in terms of the DOM, such
    user agents must still act as if events and the DOM were
    supported.</p>

    <p class="note">Scripting can form an integral part of an
    application. Web browsers that do not support scripting, or that
    have scripting disabled, might be unable to fully convey the
    author's intent.</p>

   </dd>

   <dt>Conformance checkers</dt>

   <dd id="conformance-checkers">

    <p>Conformance checkers must verify that a document conforms to
    the applicable conformance criteria described in this
    specification. Automated conformance checkers are exempt from
    detecting errors that require interpretation of the author's
    intent (for example, while a document is non-conforming if the
    content of a <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-blockquote-element">blockquote</a></code> element is not a quote,
    conformance checkers running without the input of human judgement
    do not have to check that <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-blockquote-element">blockquote</a></code> elements only
    contain quoted material).</p>

    <p>Conformance checkers must check that the input document
    conforms when parsed without a <a href="http://dev.w3.org/html5/spec/Overview.html#browsing-context">browsing context</a>
    (meaning that no scripts are run, and that the parser's
    <a href="http://dev.w3.org/html5/spec/Overview.html#scripting-flag">scripting flag</a> is disabled), and should also check
    that the input document conforms when parsed with a <a href="http://dev.w3.org/html5/spec/Overview.html#browsing-context">browsing
    context</a> in which scripts execute, and that the scripts
    never cause non-conforming states to occur other than transiently
    during script execution itself. (This is only a "SHOULD" and not a
    "MUST" requirement because it has been proven to be impossible. <a href="http://dev.w3.org/html5/spec/Overview.html#refsCOMPUTABLE">[COMPUTABLE]</a>)</p>

    
    <p>The term "HTML5 validator" can be used to refer to a
    conformance checker that itself conforms to the applicable
    requirements of this specification.</p>

    <div class="note">

     <p>XML DTDs cannot express all the conformance requirements of
     this specification. Therefore, a validating XML processor and a
     DTD cannot constitute a conformance checker. Also, since neither
     of the two authoring formats defined in this specification are
     applications of SGML, a validating SGML system cannot constitute
     a conformance checker either.</p>

     <p>To put it another way, there are three types of conformance
     criteria:</p>

     <ol><li>Criteria that can be expressed in a DTD.</li>

      <li>Criteria that cannot be expressed by a DTD, but can still be
      checked by a machine.</li>

      <li>Criteria that can only be checked by a human.</li>

     </ol><p>A conformance checker must check for the first two. A simple
     DTD-based validator only checks for the first class of errors and
     is therefore not a conforming conformance checker according to
     this specification.</p>

    </div>
   </dd>

   <dt>Data mining tools</dt>

   <dd id="data-mining">

    <p>Applications and tools that process HTML and XHTML documents
    for reasons other than to either render the documents or check
    them for conformance should act in accordance with the semantics
    of the documents that they process.</p>

    <p class="example">A tool that generates <a href="http://dev.w3.org/html5/spec/Overview.html#outline" title="outline">document outlines</a> but increases the nesting
    level for each paragraph and does not increase the nesting level
    for each section would not be conforming.</p>

   </dd>

   <dt id="editors">Authoring tools and markup generators</dt>

   <dd>

    <p>Authoring tools and markup generators must generate
    <a href="http://dev.w3.org/html5/spec/Overview.html#conforming-documents">conforming documents</a>. Conformance criteria that apply
    to authors also apply to authoring tools, where appropriate.</p>

    <p>Authoring tools are exempt from the strict requirements of
    using elements only for their specified purpose, but only to the
    extent that authoring tools are not yet able to determine author
    intent. However, authoring tools must not automatically misuse
    elements or encourage their users to do so.</p>

    <p class="example">For example, it is not conforming to use an
    <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-address-element">address</a></code> element for arbitrary contact information;
    that element can only be used for marking up contact information
    for the author of the document or section. However, since an
    authoring tool is likely unable to determine the difference, an
    authoring tool is exempt from that requirement. This does not
    mean, though, that authoring tools can use <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-address-element">address</a></code>
    elements for any block of italics text (for instance); it just
    means that the authoring tool doesn't have to verify that when the
    user uses a tool for inserting contact information for a section,
    that the user really is doing that and not inserting something
    else instead.</p>

    <p class="note">In terms of conformance checking, an editor has to
    output documents that conform to the same extent that a
    conformance checker will verify.</p>

    <p>When an authoring tool is used to edit a non-conforming
    document, it may preserve the conformance errors in sections of
    the document that were not edited during the editing session
    (i.e. an editing tool is allowed to round-trip erroneous
    content). However, an authoring tool must not claim that the
    output is conformant if errors have been so preserved.</p>

    <p>Authoring tools are expected to come in two broad varieties:
    tools that work from structure or semantic data, and tools that
    work on a What-You-See-Is-What-You-Get media-specific editing
    basis (WYSIWYG).</p>

    <p>The former is the preferred mechanism for tools that author
    HTML, since the structure in the source information can be used to
    make informed choices regarding which HTML elements and attributes
    are most appropriate.</p>

    <p>However, WYSIWYG tools are legitimate. WYSIWYG tools should use
    elements they know are appropriate, and should not use elements
    that they do not know to be appropriate. This might in certain
    extreme cases mean limiting the use of flow elements to just a few
    elements, like <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-div-element">div</a></code>, <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-b-element">b</a></code>, <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-i-element">i</a></code>,
    and <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-span-element">span</a></code> and making liberal use of the <code title="attr-style"><a href="http://dev.w3.org/html5/spec/Overview.html#the-style-attribute">style</a></code> attribute.</p>

    <p>All authoring tools, whether WYSIWYG or not, should make a best
    effort attempt at enabling users to create well-structured,
    semantically rich, media-independent content.</p>

   </dd>

  </dl><p>Some conformance requirements are phrased as requirements on
  elements, attributes, methods or objects. Such requirements fall
  into two categories: those describing content model restrictions,
  and those describing implementation behavior. Those in the former
  category are requirements on documents and authoring tools. Those in
  the second category are requirements on user agents. Similarly, some
  conformance requirements are phrased as requirements on authors;
  such requirements are to be interpreted as conformance requirements
  on the documents that authors produce. (In other words, this
  specification does not distinguish between conformance criteria on
  authors and conformance criteria on documents.)</p>

  <p>Conformance requirements phrased as algorithms or specific steps
  may be implemented in any manner, so long as the end result is
  equivalent. (In particular, the algorithms defined in this
  specification are intended to be easy to follow, and not intended to
  be performant.)</p>

  <p id="hardwareLimitations">User agents may impose
  implementation-specific limits on otherwise unconstrained inputs,
  e.g. to prevent denial of service attacks, to guard against running
  out of memory, or to work around platform-specific limitations.</p>

  </div><p class="note impl">There is no implied relationship between
  document conformance requirements and implementation conformance
  requirements. User agents are not free to handle non-conformant
  documents as they please; the processing model described in this
  specification applies to implementations regardless of the
  conformity of the input documents.</p><p>For compatibility with existing content and prior specifications,
  this specification describes two authoring formats: one based on XML
  (referred to as <a href="http://dev.w3.org/html5/spec/Overview.html#the-xhtml-syntax">the XHTML syntax</a>), and one using a <a href="http://dev.w3.org/html5/spec/Overview.html#writing">custom format</a> inspired by SGML (referred to as
  <a href="http://dev.w3.org/html5/spec/Overview.html#syntax">the HTML syntax</a>). <span class="impl">Implementations
  may support only one of these two formats, although supporting both
  is encouraged.</span></p><p class="impl" id="entity-references">The language in this
  specification assumes that the user agent expands all entity
  references, and therefore does not include entity reference nodes in
  the DOM. If user agents do include entity reference nodes in the
  DOM, then user agents must handle them as if they were fully
  expanded when implementing this specification. For example, if a
  requirement talks about an element's child text nodes, then any text
  nodes that are children of an entity reference that is a child of
  that element would be used as well. Entity references to unknown
  entities must be treated as if they contained just an empty text
  node for the purposes of the algorithms defined in this
  specification.</p><div class="impl">

  <h4 id="dependencies"><span class="secno">2.2.1 </span>Dependencies</h4>

  <p>This specification relies on several other underlying
  specifications.</p>

  <dl><dt>XML</dt>

   <dd>

    <p>Implementations that support <a href="http://dev.w3.org/html5/spec/Overview.html#the-xhtml-syntax">the XHTML syntax</a> must
    support some version of XML, as well as its corresponding
    namespaces specification, because that syntax uses an XML
    serialization with namespaces. <a href="http://dev.w3.org/html5/spec/Overview.html#refsXML">[XML]</a> <a href="http://dev.w3.org/html5/spec/Overview.html#refsXMLNS">[XMLNS]</a></p>

   </dd>

   <dt>DOM</dt>

   <dd>

    <p>The Document Object Model (DOM) is a representation — a
    model — of a document and its content. The DOM is not just
    an API; the conformance criteria of HTML implementations are
    defined, in this specification, in terms of operations on the DOM.
    <a href="http://dev.w3.org/html5/spec/Overview.html#refsDOMCORE">[DOMCORE]</a></p>

    <p>Implementations must support some version of DOM Core and DOM
    Events, because this specification is defined in terms of the DOM,
    and some of the features are defined as extensions to the DOM Core
    interfaces. <a href="http://dev.w3.org/html5/spec/Overview.html#refsDOMCORE">[DOMCORE]</a> <a href="http://dev.w3.org/html5/spec/Overview.html#refsDOMEVENTS">[DOMEVENTS]</a></p>

    <p>In particular, the following features are defined in the DOM
    Core specification: <a href="http://dev.w3.org/html5/spec/Overview.html#refsDOMCORE">[DOMCORE]</a></p>

    <ul class="brief"><li><dfn id="attr"><code>Attr</code></dfn> interface</li>
     <li><dfn id="cdatasection"><code>CDATASection</code></dfn> interface</li>
     <li><dfn id="comment-0"><code>Comment</code></dfn> interface</li>
     <li><dfn id="domimplementation"><code>DOMImplementation</code></dfn> interface</li>
     <li><dfn id="document"><code>Document</code></dfn> interface</li>
     <li><dfn id="documentfragment"><code>DocumentFragment</code></dfn> interface</li>
     <li><dfn id="documenttype"><code>DocumentType</code></dfn> interface</li>
     <li><dfn id="domexception"><code>DOMException</code></dfn> interface</li>
     <li><dfn id="element"><code>Element</code></dfn> interface</li>
     <li><dfn id="node"><code>Node</code></dfn> interface</li>
     <li><dfn id="nodelist"><code>NodeList</code></dfn> interface</li>
     <li><dfn id="processinginstruction"><code>ProcessingInstruction</code></dfn> interface</li>
     <li><dfn id="text"><code>Text</code></dfn> interface</li>

     <li><dfn id="dom-domimplementation-createdocument" title="dom-DOMImplementation-createDocument"><code>createDocument()</code></dfn> method</li>
     <li><dfn id="dom-document-getelementbyid" title="dom-Document-getElementById"><code>getElementById()</code></dfn> method</li>
     <li><dfn id="dom-node-insertbefore" title="dom-Node-insertBefore"><code>insertBefore()</code></dfn> method</li>

     <li><dfn id="dom-node-ownerdocument" title="dom-Node-ownerDocument"><code>ownerDocument</code></dfn> attribute</li>
     <li><dfn id="dom-node-childnodes" title="dom-Node-childNodes"><code>childNodes</code></dfn> attribute</li>
     <li><dfn id="dom-node-localname" title="dom-Node-localName"><code>localName</code></dfn> attribute</li>
     <li><dfn id="dom-node-parentnode" title="dom-Node-parentNode"><code>parentNode</code></dfn> attribute</li>
     <li><dfn id="dom-node-namespaceuri" title="dom-Node-namespaceURI"><code>namespaceURI</code></dfn> attribute</li>
     <li><dfn id="dom-element-tagname" title="dom-Element-tagName"><code>tagName</code></dfn> attribute</li>
     <li><dfn id="textcontent"><code>textContent</code></dfn> attribute</li>

    </ul><p>The following features are defined in the DOM Events
    specification: <a href="http://dev.w3.org/html5/spec/Overview.html#refsDOMEVENTS">[DOMEVENTS]</a></p>

    <ul class="brief"><li><dfn id="event"><code>Event</code></dfn> interface</li>
     <li><dfn id="eventtarget"><code>EventTarget</code></dfn> interface</li>
     <li><dfn id="uievent"><code>UIEvent</code></dfn> interface</li>

     <li><dfn id="event-click" title="event-click"><code>click</code></dfn> event</li>

     <li><dfn id="dom-event-target" title="dom-Event-target"><code>target</code></dfn> attribute</li>

    </ul><p>The following features are defined in the DOM
    Range specification: <a href="http://dev.w3.org/html5/spec/Overview.html#refsDOMRANGE">[DOMRANGE]</a></p>

    <ul class="brief"><li><dfn id="range"><code>Range</code></dfn> interface</li>

     <li><dfn id="dom-range-deletecontents" title="dom-Range-deleteContents"><code>deleteContents()</code></dfn> method </li>
     <li><dfn id="dom-range-selectnodecontents" title="dom-Range-selectNodeContents"><code>selectNodeContents()</code></dfn> method </li>
     <li><dfn id="dom-range-setend" title="dom-Range-setEnd"><code>setEnd()</code></dfn> method </li>
     <li><dfn id="dom-range-setstart" title="dom-Range-setStart"><code>setStart()</code></dfn> method </li>

     <li><dfn id="dom-range-collapsed" title="dom-Range-collapsed"><code>collapsed</code></dfn> attribute </li>
     <li><dfn id="dom-range-endcontainer" title="dom-Range-endContainer"><code>endContainer</code></dfn> attribute </li>
     <li><dfn id="dom-range-endoffset" title="dom-Range-endOffset"><code>endOffset</code></dfn> attribute </li>
     <li><dfn id="dom-range-startcontainer" title="dom-Range-startContainer"><code>startContainer</code></dfn> attribute </li>
     <li><dfn id="dom-range-startoffset" title="dom-Range-startOffset"><code>startOffset</code></dfn> attribute </li>

    </ul></dd>

   <dt>Web IDL</dt>

   <dd>

    <p>The IDL fragments in this specification must be interpreted as
    required for conforming IDL fragments, as described in the Web IDL
    specification. <a href="http://dev.w3.org/html5/spec/Overview.html#refsWEBIDL">[WEBIDL]</a></p>

    <p>The terms <dfn id="supported-property-indices">supported property indices</dfn> and
    <dfn id="supported-property-names">supported property names</dfn> are used as defined in the
    WebIDL specification.</p>

    <p id="float-nan">Except where otherwise specified, if an IDL
    attribute that is a floating point number type (<code title="">double</code>) is assigned an Infinity or Not-a-Number
    (NaN) value, a <code><a href="http://dev.w3.org/html5/spec/Overview.html#not_supported_err">NOT_SUPPORTED_ERR</a></code> exception must be
    raised.</p>

    <p>Except where otherwise specified, if a method with an argument
    that is a floating point number type (<code title="">double</code>)
    is passed an Infinity or Not-a-Number (NaN) value, a
    <code><a href="http://dev.w3.org/html5/spec/Overview.html#not_supported_err">NOT_SUPPORTED_ERR</a></code> exception must be raised.</p>

   </dd>

   <dt>JavaScript</dt>

   <dd>

    <p>Some parts of the language described by this specification only
    support JavaScript as the underlying scripting language. <a href="http://dev.w3.org/html5/spec/Overview.html#refsECMA262">[ECMA262]</a></p>

    <p class="note">The term "JavaScript" is used to refer to ECMA262,
    rather than the official term ECMAScript, since the term
    JavaScript is more widely known. Similarly, the <a href="http://dev.w3.org/html5/spec/Overview.html#mime-type">MIME
    type</a> used to refer to JavaScript in this specification is
    <code title="">text/javascript</code>, since that is the most
    commonly used type, <a href="http://dev.w3.org/html5/spec/Overview.html#willful-violation" title="willful violation">despite it
    being an officially obsoleted type</a> according to RFC
    4329. <a href="http://dev.w3.org/html5/spec/Overview.html#refsRFC4329">[RFC4329]</a></p>

   </dd>

   <dt>Media Queries</dt>

   <dd>

    <p>Implementations must support some version of the Media Queries
    language. <a href="http://dev.w3.org/html5/spec/Overview.html#refsMQ">[MQ]</a></p>

   </dd>

   <dt>URIs, IRIs, IDNA</dt>

   <dd>

    <p>Implementations must support the semantics of <a href="http://dev.w3.org/html5/spec/Overview.html#url" title="URL">URLs</a> defined in the URI and IRI specifications,
    as well as the semantics of IDNA domain names defined in the
    <cite>Internationalizing Domain Names in Applications
    (IDNA)</cite> specification. <a href="http://dev.w3.org/html5/spec/Overview.html#refsRFC3986">[RFC3986]</a>
    <a href="http://dev.w3.org/html5/spec/Overview.html#refsRFC3987">[RFC3987]</a> <a href="http://dev.w3.org/html5/spec/Overview.html#refsRFC3490">[RFC3490]</a>

   </p></dd>

  </dl><p>This specification does not <em>require</em> support of any
  particular network protocol, style sheet language, scripting
  language, or any of the DOM specifications beyond those described
  above. However, the language described by this specification is
  biased towards CSS as the styling language, JavaScript as the
  scripting language, and HTTP as the network protocol, and several
  features assume that those languages and protocols are in use.</p>

  <p class="note">This specification might have certain additional
  requirements on character encodings, image formats, audio formats,
  and video formats in the respective sections.</p>

  </div><h4 id="extensibility"><span class="secno">2.2.2 </span>Extensibility</h4><p class="XXX annotation"><span><a href="http://www.w3.org/html/wg/tracker/issues/41">ISSUE-41</a> (Decentralized-extensibility) blocks progress to Last Call</span></p><p>HTML has a wide number of extensibility mechanisms that can be
  used for adding semantics in a safe manner:</p><ul><li>Authors can use the <code title="attr-class"><a href="http://dev.w3.org/html5/spec/Overview.html#classes">class</a></code>
   attribute to extend elements, effectively creating their own
   elements, while using the most applicable existing "real" HTML
   element, so that browsers and other tools that don't know of the
   extension can still support it somewhat well. This is the tack used
   by Microformats, for example.</li>

   <li>Authors can include data for inline client-side scripts or
   server-side site-wide scripts to process using the <code title="attr-data-*"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-data">data-*=""</a></code> attributes. These are
   guaranteed to never be touched by browsers, and allow scripts to
   include data on HTML elements that scripts can then look for and
   process.</li>

   <li>Authors can use the <code title="meta"><a href="http://dev.w3.org/html5/spec/Overview.html#meta">&lt;meta name=""
   content=""&gt;</a></code> mechanism to include page-wide metadata by
   registering <a href="http://dev.w3.org/html5/spec/Overview.html#concept-meta-extensions" title="concept-meta-extensions">extensions to the
   predefined set of metadata names</a>.</li>

   <li>Authors can use the <code title="attr-hyperlink-rel"><a href="http://dev.w3.org/html5/spec/Overview.html#attr-hyperlink-rel">rel=""</a></code> mechanism to annotate
   links with specific meanings by registering <span title="concept-rel-extensions"> extensions to the predefined set of
   link types</span>. This is also used by Microformats.</li>

   <li>Authors can embed raw data using the <code title="script"><a href="http://dev.w3.org/html5/spec/Overview.html#script">&lt;script type=""&gt;</a></code> mechanism with a custom
   type, for further handling by inline or server-side scripts.</li>

   <li>Authors can create <a href="http://dev.w3.org/html5/spec/Overview.html#plugin" title="plugin">plugins</a> and
   invoke them using the <code><a href="http://dev.w3.org/html5/spec/Overview.html#the-embed-element">embed</a></code> element. This is how Flash
   works.</li>

   <li>Authors can extend APIs using the JavaScript prototyping
   mechanism. This is widely used by script libraries, for
   instance.</li>


  </ul><div class="impl">

  <hr><p>Vendor-specific proprietary user agent extensions to this
  specification are strongly discouraged. Documents must not use such
  extensions, as doing so reduces interoperability and fragments the
  user base, allowing only users of specific user agents to access the
  content in question.</p>

  <p>If such extensions are nonetheless needed, e.g. for experimental
  purposes, then vendors are strongly urged to use one of the
  following extension mechanisms:</p>

  <p>For markup-level features that can be limited to the XML
  serialization and need not be supported in the HTML serialization,
  vendors should use the namespace mechanism to define custom
  namespaces in which the non-standard elements and attributes are
  supported.</p>

  <p>For markup-level features that are intended for use with
  <a href="http://dev.w3.org/html5/spec/Overview.html#syntax">the HTML syntax</a>, extensions should be limited to new
  attributes of the form "<code title="">x-<var title="">vendor</var>-<var title="">feature</var></code>", where
  <var title="">vendor</var> is a short string that identifies the
  vendor responsible for the extension, and <var title="">feature</var> is the name of the feature. New element names
  should not be created. Using attributes for such extensions
  exclusively allows extensions from multiple vendors to co-exist on
  the same element, which would not be possible with elements. Using
  the "<code title="">x-<var title="">vendor</var>-<var title="">feature</var></code>" form allows extensions to be made
  without risk of conflicting with future additions to the
  specification.</p>

  <div class="example">

   <p>For instance, a browser named "FerretBrowser" could use "ferret"
   as a vendor prefix, while a browser named "Mellblom Browser" could
   use "mb". If both of these browsers invented extensions that turned
   elements into scratch-and-sniff areas, an author experimenting with
   these features could write:</p>

   <pre>&lt;p&gt;This smells of lemons!
&lt;span x-ferret-smellovision x-ferret-smellcode="LEM01"
      x-mb-outputsmell x-mb-smell="lemon juice"&gt;&lt;/span&gt;&lt;/p&gt;</pre>

  </div>

  <p>Attribute names beginning with the two characters "<code title="">x-</code>" are reserved for user agent use and are
  guaranteed to never be formally added to the HTML language. For
  flexibility, attributes names containing underscores (the U+005F LOW
  LINE character) are also reserved for experimental purposes and are
  guaranteed to never be formally added to the HTML language.</p>

  <p class="note">Pages that use such attributes are by definition
  non-conforming.</p>

  <p>For DOM extensions, e.g. new methods and IDL attributes, the new
  members should be prefixed by vendor-specific strings to prevent
  clashes with future versions of this specification.</p>

  <p>All extensions must be defined so that the use of extensions
  neither contradicts nor causes the non-conformance of functionality
  defined in the specification.</p> <!-- thanks to QA Framework -->

  <div class="example">

   <p>For example, while strongly discouraged from doing so, an
   implementation "Foo Browser" could add a new IDL attribute "<code title="">fooTypeTime</code>" to a control's DOM interface that
   returned the time it took the user to select the current value of a
   control (say). On the other hand, defining a new control that
   appears in a form's <code title="dom-form-elements"><a href="http://dev.w3.org/html5/spec/Overview.html#dom-form-elements">elements</a></code>
   array would be in violation of the above requirement, as it would
   violate the definition of <code title="dom-form-elements"><a href="http://dev.w3.org/html5/spec/Overview.html#dom-form-elements">elements</a></code> given in this
   specification.</p>

  </div>

  <p>When adding new <a href="http://dev.w3.org/html5/spec/Overview.html#reflect" title="reflect">reflecting</a> IDL
  attributes corresponding to content attributes of the form "<code title="">x-<var title="">vendor</var>-<var title="">feature</var></code>", the IDL attribute should be named
  "<code title=""><var title="">vendor</var><var title="">Feature</var></code>" (i.e. the "<code title="">x</code>"
  is dropped from the IDL attribute's name).</p>

  <hr><p>When vendor-neutral extensions to this specification are needed,
  either this specification can be updated accordingly, or an
  extension specification can be written that overrides the
  requirements in this specification. When someone applying this
  specification to their activities decides that they will recognize
  the requirements of such an extension specification, it becomes an
  <dfn id="other-applicable-specifications" title="other applicable specifications">applicable
  specification</dfn> for the purposes of conformance requirements in
  this specification.</p>
  <!-- http://www.w3.org/mid/17E341CD-E790-422C-9F9A-69347EE01CEB@iki.fi -->

  <p class="note">Someone could write a specification that defines any
  arbitrary byte stream as conforming, and then claim that their
  random junk is conforming. However, that does not mean that their
  random junk actually is conforming for everyone's purposes: if
  someone else decides that that specification does not apply to their
  work, then they can quite legitimately say that the aforementioned
  random junk is just that, junk, and not conforming at all. As far as
  conformance goes, what matters in a particular community is what
  that community <em>agrees</em> is applicable.</p>

  <hr><p>User agents must treat elements and attributes that they do not
  understand as semantically neutral; leaving them in the DOM (for DOM
  processors), and styling them according to CSS (for CSS processors),
  but not inferring any meaning from them.</p>

  <p>When support for a feature is disabled (e.g. as an emergency
  measure to mitigate a security problem, or to aid in development, or
  for performance reasons), user agents must act as if they had no
  support for the feature whatsoever, and as if the feature was not
  mentioned in this specification. For example, if a particular
  feature is accessed via an attribute in a Web IDL interface, the
  attribute itself would be omitted from the objects that implement
  that interface — leaving the attribute on the object but
  making it return null or throw an exception is insufficient.</p>

  </div><h3 id="case-sensitivity-and-string-comparison"><span class="secno">2.3 </span>Case-sensitivity and string comparison</h3><p>Comparing two strings in a <dfn id="case-sensitive">case-sensitive</dfn> manner means
  comparing them exactly, code point for code point.</p><p>Comparing two strings in an <dfn id="ascii-case-insensitive">ASCII case-insensitive</dfn>
  manner means comparing them exactly, code point for code point, except
  that the characters in the range U+0041 to U+005A (i.e. LATIN
  CAPITAL LETTER A to LATIN CAPITAL LETTER Z) and the corresponding
  characters in the range U+0061 to U+007A (i.e. LATIN SMALL LETTER A
  to LATIN SMALL LETTER Z) are considered to also match.</p><p>Comparing two strings in a <dfn id="compatibility-caseless">compatibility caseless</dfn>
  manner means using the Unicode <i>compatibility caseless match</i>
  operation to compare the two strings. <a href="http://dev.w3.org/html5/spec/Overview.html#refsUNICODE">[UNICODE]</a></p><p>Except where otherwise stated, string comparisons must be
  performed in a <a href="http://dev.w3.org/html5/spec/Overview.html#case-sensitive">case-sensitive</a> manner.</p><div class="impl">

  <p><dfn id="converted-to-ascii-uppercase" title="converted to ASCII uppercase">Converting a string to
  ASCII uppercase</dfn> means replacing all characters in the range
  U+0061 to U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z)
  with the corresponding characters in the range U+0041 to U+005A
  (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z).</p>

  <p><dfn id="converted-to-ascii-lowercase" title="converted to ASCII lowercase">Converting a string to
  ASCII lowercase</dfn> means replacing all characters in the range
  U+0041 to U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL
  LETTER Z) with the corresponding characters in the range U+0061
  to U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL LETTER Z).</p>

  </div><p>A string <var title="">pattern</var> is a <dfn id="prefix-match">prefix match</dfn>
  for a string <var title="">s</var> when <var title="">pattern</var>
  is not longer than <var title="">s</var> and truncating <var title="">s</var> to <var title="">pattern</var>'s length leaves the
  two strings as matches of each other.</p><h3 id="utf-8"><span class="secno">2.4 </span>UTF-8</h3><p>When a user agent is required to <dfn id="decoded-as-utf-8-with-error-handling" title="decoded as UTF-8,
  with error handling">decode a byte string as UTF-8, with error
  handling</dfn>, it means that the byte stream must be converted to a
  Unicode string by interpreting it as UTF-8, except that any errors
  must be h</p></body></html>